Just some observations, attempts at making sense of the world. I may be wrong. I admit that these are opinions, based on my experiences.
Liberals tend to believe that people are inherently good. Conservatives tend to believe that people are inherently bad. Liberals believe that evil is a result of negative environmental conditions that cause people to deviate from their inner badness. Conservatives believe that goodness is a result of negative environmental conditions that cause people to repress their inner badness.
Compare, for example, “Spare the rod and spoil the child,” to, say, any liberal parent you’ve ever met.
Or compare the conservative reaction to ISIS (“Bomb them until they convert to Christianity or all die,”) to the liberal, “To defeat ISIS, we need more jobs for people in the Middle East.”
Liberals are generally more pleasant to be around, even if they are occasionally delusional.
In general, both sides tend to act like there exists one single, agreed-upon definition of what “good” is, even though a conversation with virtually any other human being on the face of this planet will quickly reveal that this is entirely untrue, as that other person holds forth that all sorts of horribly dumb ideas are good and that all of your best traits are really really bad.
Conservatives claim they know what “good” is because “God said so,” and anyone who doesn’t agree with them about what God says is Obviously Evil. It’s not much of a position, but at least you can defend it if you accept the initial premise.
Liberals think that everyone else sees “good” and “bad” the same way they do just because to do otherwise would meant that other people are doing things that liberals see as “bad” even without negative environmental effects, which blows the whole shebang out of the water. Which is really kind of annoying when someone really and truly doesn’t get that you actually do see XYZ as good rather than the result of some horrible trauma that made you do bad, though that’s still not as bad as conservatives dropping bombs on you.
Of course, in reality, most people try to do “good” as they themselves see it, moderated somewhat by their genetic inclinations and culture. The guys in ISIS really and truly do see themselves as good guys, while homeless people fret over the sin of stealing a shopping cart so they have a place to put their stuff.
I wouldn’t go so far as to say that all morality is relative, you can’t judge anyone else, etc. etc. I would say that our basic understanding of “good” and “evil” people/actions/behaviors is very specific to our own particular culture/subculture/immediate group of friends & family, and probably just isn’t a very meaningful way of understanding the actions of people outside of those groups.