The Star Wars fans aren't missing that they're dressing up as the bad guys. People dress up as evil characters all the time.

Are you saying people are mistakenly thinking that the stormtroopers are “good guys” and wouldn’t play them if they’d realized they are “bad guys”?

People have been consciously cosplaying as villains for decades because pretending to be evil can be fun as hell; I'm not sure what that's supposed to illustrate, really.

You all (you, nitwit005, andrewstuart) make a very good point. Besides, having a red helmet with "Make The Empire Great Again" would be hilarious.