Have you ever thought about why people who wear face concealing masks/helmets are always evil? Examples: stormtroopers, Darth Vader, Cobra Commander, all of the soldiers in Cobra, uhm, Scarecrow, Dr. Doom? I think that's all I've got, but feel free to contribute your own!
Hmmm... But Iron Man isn't evil. Nevermind.
Also, people with mustaches are generally portrayed as evil.