Why do villains always appear so sinister and devious?

For instance, The Joker from Batman or Whiplash from Iron Man (obvious influence for my question) – the good guys always wear the “good guy” cape and the bad guys are always dressed in dark, sneering away with a grin on their face. I know these are based off of the original comics (in which it fits in with the whole original point of a superhero that fights crime) but it seems like even yet in most modern-day movies it never seems like a side vs. side situation, there’s an evident good vs. evil.

In reality, it doesn’t always work that way. There’s a disagreement on two neutral sides and a fight as a result and only with one’s own judgment, position and reasoning does a “good” and “bad” side come about. Very few movies actually pull it off – or they’ll show you what it’s like to be in the villain’s mind which makes you feel inclined to sympathize with them, but I feel it’s never a neutral sided fight.

Why is that? Do you really think villains actually thrive on being or seeing themselves as evil? In their mind, aren’t they doing something just as good as the hero?