He's the main protagonist of the Mario series so not really. However, in Donkey Kong 2, Mario is actually the main antagonist of that game. some people think that he is because he does-
- family abuse (Luigi)
- flirts with many girls (besides peach)
- animal abuse (Yoshi's and old Donkey Kong games)
- serial killer (he kills innocent turtles and living mushrooms AKA all the things that walk toward him)
if you watch his behavior it can be quite obvious. these are several reasons, but it all depends on how you look at it.