This is due to two powerful factors: 1) Americans as a general rule do not like to critique anything ever, hence why shit-awful movies like The Avengers and Transformers always make more money than anything worthy. And 2) A serious analysis of evil as a concept leads to discomforting revelations.
Let's start slow - Who do you hate? Just of the top of your head, someone you wouldn't mind seeing creamed by a bus? If you answered at all you've demonstrated evil, naturally, but that brings us to our next question: Why do you hate this person?
Have they done something to you? They probably have, since people are so invariably shitty to one another. Or, to go into murkier waters, has this person actually not done much of anything to you directly but something about their existence just offends you? Maybe they're more successful, maybe they're less successful but not bothered by it.
Maybe they're just different from you...
All of these reasons are evil, there's no denying. At least not by anyone who matters. But why would you have these reasons in the first place? Why should the material fortunes - or lack thereof - of another person concern you in such a way?
Because society told you to. Whether your parents or television or the other kids in your neighborhood, you were conditioned to hold these wicked views by others. Racism is often explained this way and while it doesn't touch on the depth of human atavism it at least gets the gist of things. Whatever malice you hold for others, if not founded in a direct personal experience, was fostered by the world around you as culturally normative behavior.
Here we move out of the comforting Neoplatonist definitions of evil and into the more grimly rationalist view. The idea that this is not in fact the best of all possible worlds, that the harmony we think we see in Nature is just an anthropocentric delusion, and that Evil is not an aberration in the grand scheme of things but rather the banal starting point.
[T]here’s only one evil, it suffuses everything we see, and while one might do less harm than the other, each of its warring parts is still fundamentally the same thing. Donald Trump’s frenzied populism couldn’t exist without the suffocating liberal condescension of a Hillary Clinton; nobody would ever vote for Clinton if it weren’t for the looming threat of a Trump.That which is good, or at least not-evil, is not the baseline but rather the achievement. The long and ugly march of human history bears this out, though it is too often taken as a given. The old feudal hierarchies of Europe did not so much progress to liberal democracy as they were dragged kicking and screaming. As a labor activist once said, "It's never been easy," because every little improvement came from a confrontation with entrenched power that always sees its own self-perpetuation as the most important task at hand. Whether the power is claimed by divine right or meritocratic ladder climbing, it always seeks to preserve "order" at the expense of those outside its hallowed halls.
Evil, then, is both the natural state of existence and the resistance to changing for the better.