The reason for confusion over the terms ethics and morals is very simple. They are confused. There are the pure ethical systems of philosophy based upon reason. There are the pure moral systems of religion based purely upon revelation or dogma. And then there is what most of the rest have, a salad bar selection from ethical and moral systems.
The salad bar approach is perhaps most easily illustrated by pointing out that in the Bible an abortion is mentioned only once and then requires only a small compensation. On the other hand, the Hippocratic Oath expressly prohibits abortions. Obviously it is not only easy to pick and choose but to reverse obvious sides.
The two differ in their roots. Religions that have one god (post Babylonian Hebrews) or effectively one god (Marduk of Babylon or Ahura Mazda of the Zorastrians) associate their principles of social behavior to be what please their god. Those which have a plethora of more or less equal gods (Greeks and Romans) or too many to keep track of (Hindus) do not attribute social norms to their gods.
Now all are in the "don't piss off the god(s)" mode of course but where it is easy to conceive of a single god handing down ten commandments, the Greek pantheon would still be fighting over which ten to include. Also the single and dominant gods tend to be fighting some more or less equally powerful and evil god in some form such as the image of Satan. Although this was grafted on to Christianity several centuries after it started, when the Hebrews expunged their other gods they replace them with the hordes of demons from which Marduk protected his worshippers.
Thus from the Greeks we have the first attempt at code of conduct, ethics if you will, to replace the competing demands of so many individual gods. (Bhudda was more likely the first but that is another discussion and they were not clearly connected.) Socrates taught rules of conduct for both the individual and the government. Examination of the charges against him were not that he taught contrary to all the gods but contrary to the demands of the chief gods of Athens risking their displeasure. It was not their concern what Socrates believed as the gods would deal with him individually. Rather that a large number of the young were following him and that would bring disfavor upon the city.
Later Aristotle managed to avoid dying for his attempt at a god neutral ethics although the Greeks were preoccupied with Philip of Macedon. So the story goes, Aristotle died for keeping Philip waiting. In any event, this idea spread to Rome as it also had an "impossible to please" pantheon of gods.
Thus it is quite true that the Greeks and Romans were amoral as their actions, other than ritual worship, were not governed by the absolutes of any god. For example Rome could have been a warrior culture had Mars dominated the other gods. As it was the temple of Mars was only open when the empire was at war and closed otherwise. Thus the god was only called upon in time of need, very like a Catholic with a fish bone in his throat and St. Blaise.
Eventually a single god system that was ultimately imposed upon the Roman Empire. Little survives of the first single god system to become popular in Rome, the Cult of Mithra (which was centered in Tarsus at the time of Paul.) We do not know what their particular moral code might have been as most records of them were eliminated by the later Christians after the Christians adopted their rituals and customs and beliefs in to Christianity. For example there was the virgin birth, born in and buried in a cave, resurrection, even down to ceremonies in caves and Vatican Hill being sacred to them.
Christianity did have moral teachings, many of them, and of course they conflicted. They settled their theological and moral differences by killing off the opposition such as the Sunday slaughters in Constantinople. Perhaps this was good as it lead Constantine to take control of the various Christians and start to impose some sort of order. But the order he imposed was merely that of accepting the beliefs and morals of the most powerful sects. For example, the teachings of Augustine were included as at the time it was not known he was a liar in claiming to have converted a race of headless men and a race of cyclops.
It probably would not have mattered even if it were known as power determined doctrine and moral teachings. It is easy to show doctrinal changes, forgeries, and other forms of fraud, lies, treachery and even murder to impose the present limited forms of doctrinal variations we have. It is more difficult to show changes in moral teachings.
It is left for the student of comparative religion to perform the trivial exercise of showing the current prohibitions of some sects against drinking, dancing, smoking and the like are clearly the inventions of men in the name of a god. It is less easy to show the changes in morality. Most likely this is due to there being a certain reverence for what was considered to be an early gospels (there were close to two hundred) but the moral teachings of a losing teacher like Origen were easier to burn.
We are often required to read between the lines to see that even the behavior required by the Christian God is not clear but also a matter of the teachings of men. For example, we all know the use of the bible to approve slavery in this country. And of course it was never condemned by Jesus or his disciples although other teachers had called it wrong and even outlawed it centuries before him.
Compare that lack of condemnation to the condemnation in Acts of consorting with prostitutes. It is very clear and I presume anyone raised Christian knows of that condemnation. Of course what is rarely mentioned is that the condemnation was to avoid incest as it says. But between the lines, what is not said, is that it was not condemned for Christians to sell their children into prostitution. After all, one of the main points of the gospels was that Jesus consorted with prostitutes. It would have been difficult to condemn that per se.
In being confronted with the belief that either the life of Christ just happened to match the stories about Mithra from a century earlier or that Paul, a Jew, substituted Jesus for Mithra and told the same stories about him, the latter is by far the most likely. And in noting that Paul mentions not one of the teachings of Jesus from the four approved gospels. Rather he refers to the mysteries of virgin birth, resurrection and the like.
This has been a long digression. The point of this is that ethical systems are the result of a single person such as Socrates, Hippocrates, or Aristotle attempting to develop functional guidelines for a particular profession or activity such that at least the simpler problems are worked out. Morals come from a random sequence of victors at particular points in time over doctrinal issues and the morality that came from them.
For example the doctrinal issues of Augustine survived and thus did his early discourse upon lying, even though we is now known to be a bald face liar. But is the survival of teachings against lying something that should not be part of our morality? Of course not. It is the creation of a man to address a particular issue, thus it is a matter of ethics. It is not a matter of sin or evil it is a matter of personal integrity. And for those who would hold he was repeating something moral from the ten commandments, his writings were against lies of omission and commission for the purpose of inspiring the faithful, much as he did with his headless men and cyclops.
And much of the strangely perverted sexual morality he taught, common today, strange then and for centuries before, is not surprisingly missing from the teachings of Jesus. This is simply one example of the followers of Augustine winning the doctrinal wars and finding the ethical teachings of its leader being accepted as god given.
More clearly, at that time, there were a half dozen interpretations of what Jesus was. Augustine was not in the "god and son of god" group. Had a different group triumphed later, this Jesus could have been the adopted son of god, a teacher, a prophet or any of the other ideas as tortured as the "trinity" we have inherited from the political victory of the sect pushing that idea.
Clearly those who do follow what appear to be the earliest collection of teachings of Jesus are today considered the strangest people. Simple things like turning the other cheek, rather than being viewed as the foolishness of a hopeless theorist, are steeped in doubletalk so that 1) it sounds like intelligent teaching and 2) people do not have to take the teaching either literally or seriously. Those who would turn the other cheek are only for the movies while righteous anger mounts to a dramatic conclusion, the scourging of the money changers in the temple from that particular religious dramatization.
The better known examples of this process come from the separation of the Eastern and Western Catholic Churches and the separation of the Protestant religions from the Western Catholic Church and from each other. The first great break was the Bishop of Rome suffering the first delusion of the many who would follow him of restoring the Roman Empire. In the separation of the Western Church the Popes created morality and immorality with the same elan as did the Eastern bishops. In the blink of an eye Christ has taught is was immoral to charge interest and hundreds of other on and off items of personal ethics converted to the moral order of god.
When Martin Luther decided the Bishop of Rome was having problems determining the exact status of holes in the ground and lead the way to creating even more revelations direct from the word of God and Jesus in a bible that had no particular merit in translational accuracy. Of course there were translations into the language of the people but they were little more than desired translations. The virgin Mary was not corrected to the young woman Mary. Christ's death on the cross was not corrected to his death on the stake (as in Vlad the Impaler's method.)
The basic religious traditions were preserved but variations upon morality were introduced. Not from the great pretension of having discovered something new in a poor translation. Rather it was finding the person's personal proclivities in some words in this now readable bible. John Calvin found his theology and along with it, his personal ethics were transposed to the teachings of god.
Given what evidence we do have it is hard to imagine that at some point there really was a god making revelations. Rather there were constant factions in those who have a one or a few gods as to exactly what they wanted to avoid wrath. Clearly one of those gods wanted to be considered the primary god and to be put ahead of all the other gods as in his first commandment to Moses. As archaeology tells us this god had a wifely god and there are clear mentions to other functional gods, the idea of monotheism from the beginning is hard to accept. Clearly the Moses faction (despiter there is no evidence or reason to believe in his existence) at one point won out over other factions and had the power to eliminate other writings and preserve their own. They were even able to (almost) enforce the "no graven images" precept to remove all the images of the great horned god Yahweh.
But in all of this, the rest of the commandments that survived under the Yahweh followers were clearly their idea of what their god wanted but in fact the invented ethics of men raised to the word of a god. In the Hebrew, early Christianity, the Catholic period and the Reformation periods we can clearly see the ease with which a single god can be satisfied and the winners can impose their personal ethics upon the visage of a god.
Thus we have ethical systems clearly developed by people, see the ethics committees of the various professions if you have any further doubts. We have the ethics of people who were part of religious movements that have been elevated to the word of a god. But we still have a problem. They all appear to have so much in common. Yes, but, only if you do not pay attention to the details. But if you pay attention to the details in the right way it does match a broader theme.
For example we have the problem with adultery today. If we go further back we find no problem with mistresses and prostitution. If we continue further back we find no problem with multiple wives and concubines (contract prostitutes.) Going back further we find the only general requirement to be that sexual activity has to be within the clan even if that means parents and children.
In that generality we can look at the behavior of other social mammals and of primitive social groups existing today. In that sense we see the rule of, thou shalt not copulate with strange tribes. In that light we can find, thou shalt not kill members of your own social group unless they become a danger to that group.
The variations upon general principles such as these are the personal ethics elevated to orders from a god. The point can hardly be made that morals evolve and still attribute their source to an all knowing divinity.
If I may be so bold as to observe, any wise deity, anyone sent from any god to alleviate human suffering would have taught, thou shalt not become a leader of they fellow man. Doing so risks imposing a personal ethic upon others and to satisfy the people it needs be attributed to something greater than the leader.
But such a teaching is impossible as it is human nature to form groups and that a leader emerge for that group. That is as it is for all social mammals. We are not all that unique in the basics. But we do make complex distinctions that cloud what we are really doing.
What a religious "leader" would claim to be a discovery about a god is no more than that leader finding a way to find support for his personal ethic.
Thus in ethics we are seeing what a person or select group thinks through to its consequences to make it easier to get through the hard decisions in life. A religion is that same personal ethic but attributed to some superhuman entity by the person who held it all along. But this is not the average person.
Unless one becomes not only a student of but also insists upon applying a particular ethical or moral system then one has no SYSTEM of ethics or morals. Most people take a good idea here, another idea there, add them with a sentence of guidance from a parent when a child and think they have more than a salad bar. This is not to say that salad bars are all that bad. The Chinese have a tendency to pick and choose deliberately and be rather proud of their selections.
Americans generally do not realize they are also of the salad bar mentality unless they are regular Sunday School attendees and work to apply the doctrines they are taught. And even then, most religions do not have any but the broadest guidelines for what is taught in such schools and much of the personal "salad bar" of the teacher comes in. Thus it is not much of a system either.
Consider the abortion issue again. Even the most rabid pro-life person who considers abortion to be murder in a moral sense, does not consider the woman who pays for that murder to be guilty when if she had paid for the murder of the father they would call it the vilest of murders.
Those who will support pro-choice will argue a woman has the right to do with her body what she will yet will not defend a woman's right to use her drug of choice.
Picking and choosing from the salad bar of ethics and morality is a very popular hobby. It is not as though it is difficult to find some moral or ethical principle to justify most anything anyone wants to do. Note the difference between principle and system. It is nearly impossible to find any system that supports everything one wants to do. It is almost trivial to find a principle in some system or other to justify anything one wants to do.
Yes, I know, I have just spent only some 3000 words demonstrating both ethics and morality are of human origin, given the real source of both, an identified the fallacy of confusing systems with principles within systems as having validity and describing what most people do with both. Rather concise I thought.
It is not as though it is that hard to see if only one dispassionately examines all inconsistencies in statements about morals and ethics and resolve the inconsistencies to their root causes.
In any event, an ethical can be clearly attributed to men. A moral system can be clearly attributed to men who discover a god agrees with them. There is no known case of a moral teacher, including Jesus who was the Christ, who did not discover what he wanted to find in some god in that none of them, not even he, deviated from prior teachings as reference, only a new meaning he found in them.
Such is human nature. Truly a wise and benevolent deity would advise both believer and non not to become leaders of men. They are not worthy.