"i think being able to tell someone to be a super villain just from looking at them comes down to perspective, opinion and prejudice ("he has a goatie, so he must be evil" like that)
what might look like a shady fellow to you might be some innocent bystander and vice versa
personally i think the best villains are the ones that look like they aren't evil but have some evil atmosphere about them and the ones who were driven into insanity or evilness and just look crazy."

- I agree with you on most part only you are relating to much on real life situations We are talking about supervillains here from cartoons,comic books, videogames and movies, they are generally designed to look evil and again I don't think anyone of the entries has succeeded in depicting something evil, sure there are a couple of great entries with great designs but the challenge is called supervillain, not great characters, nice lighting or shading.

I agree with you however that the people who choose existing characters didn't have to show the evil part as the originals did because they are already imprinted in our brain as being evil