Even though people may not be deliberately invoking religion when they talk about evil, that is in fact what they're doing. Behavior may be concretely described as unlawful, destructive, disruptive to social order, but evil? That's always going to be up to interpretation, and there is simply no single authority on Earth that can dictate what is evil and what is not. That's what brings it back to a religious argument--something greater than us must be the arbiter of those distinctions.
The example you gave with the ancient Greeks actually helps make my point: they considered disorder evil, but that doesn't mean it is. Even today, we recognize some amount of disorder as beneficial to society. Definitions change. Subjective labels like "evil" serve very little purpose when analyzing motivation or consequences.
Your closing phrase, "evil as a given behavior," doesn't even make sense to me, because I cannot describe any particular behavior as objectively "evil." I could describe it as unethical within a given ethical framework, immoral by the standards of a given society, physically or emotionally destructive or disruptive, but not "evil."
You're basically saying it's up to God, or only the theologians, to define evil? No other definition would be valid?
Of course the term is subjective. And, if the Greeks considered disorder evil, who am I to say it wasn't? It certainly seems logical to me that a society would fear chaos and the things that come from it. Evil things can't come from chaos and disorder? Chaos and disorder are often the results of natural disasters, which some Christians even today blame on Evil. So, why shouldn't a society call disorder evil and try to prevent it?
I'm saying there is no definition of "evil" that is universally valid, and therefore a question such as "Was Hitler actually evil?" is meaningless and serves little purpose other than the asserting the moral superiority of those who ask and answer it.
Who "causes" these evil things, who wrought them upon the Earth, is a question for theologians. Making evil empirical and trying to explain it within the empirical world is the job of science.
How would you empirically define "evil"?
Why God would let Hitler come to power is not an empirical quesiton. There is Evil in the world is an answer. How a man could become Adolph Hitler, how a society could fall under his spell, and why he acted as he did are empirical questions. And, it is a study of evil. I don't think anyone would dispute that.
No, it is not a "study of evil." It is a study of history. All the things you mentioned are worth studying, but none of them have anything to do with empirically quantifying evil.
Many political and social terms are subjective. What exactly is sociopathic behavior? What is paranoia? What is partisanship? There can be valid degress of each. So, just because evil is a subjective term doesn't mean there aren't reliable and valid definitions of it. Or even recognized variations in degress of it. The word "evil" gets overused, politicized, and has been watered-down in popular use. But if one wanted to really bear down and conceptualize and operationalize a scientifically reliable and valid definition, one could. Indeed, one could create several. All good.
Sociopathy and paranoia are psychological terms with definitions established by the medical community. Partisanship is easier to define than you think--it is little more than a trend of behavior in which a political almost always acts in accordance with the rest of his party.
You could not scientifically define "evil." All you could do is come to a consensus among a particular group of people, agreeing that they believe something to be evil (or not.) This, however, does not make the act in question evil. Instead, it only reflects the beliefs of those asserting such an opinion.
If we dismiss all definitions as merely subjective, then we're saying the subject can't be discussed at all. We have no common ground other than just agreeing that it exists in an abstract form. In religion, this may be fine because it's the existence of evil itself that's more important than any one empirical defintion. Any evil, however defined, must be reconciled with the existence of God.
Any definition of "evil" is inherently subjective, because what each person believes to "evil" comes from no central authority. That is why questions of what is evil and what isn't are relegated to the purview of theologians, who can claim divine authority on the matter.
Pornography is hard to define. It is highly subjective. But we don't walk away from operationalizig it. We have legal defintions of it anyway. We dispute them, refine them as mores change, but we nonetheless have laws that are at least acceptable to a majority of those under the various jurisdictions which enforce them.
Ah, but we have legal definitions of what pornography is! We have no legal definition of "evil."
When I say, "Evil is a given behavior," I mean I can define the concept and operationalize it. That is the basis of any scientific method. It's not necessarily always about "why" evil exists. That is philosophical and theological.
Sometimes it's about explaining the manifestation of evil. It's employment, and how mankind got to that state. How what's evil even changes over time. Today, we would consider owning slaves evil. Yesterday, some people justified it by saying it was in the Bible.
You have consistently failed to answer my basic point: who defines what is "evil"? When it comes to Hitler, it isn't even a relevant question. You cannot answer "Was Hitler actually evil?" What you can do is document his particular crimes, which most would agree are reprehensible and have earned him eternal infamy.
I must say, this notion that one can scientifically quantify "evil" is pretty bizarre to me.