Definition of VILLAIN
1
: villein
2
: an uncouth person : boor
3
: a deliberate scoundrel or criminal
4
: a character in a story or play who opposes the hero
5
: one blamed for a particular evil or difficulty
Because the word villain implies that it is bad for the sake of bad. At least to me it does. You could make an argument that 4 does not mean it is evil but it still means that they do not serve the right and proper sid eof things.