It's not so much that wearing a ski mask is illegal (though that's true in some cities) but it demonstrates you are deliberately committing the real crime, not an accident. You can wear a mask. You can tell a bank teller "I'm here to make a large withdrawal." Doing both at the same time? Good luck convincing the jury you were just trying to hide from your wife while getting some cash for a friends bachelor party.
> but it demonstrates you are deliberately committing the real crime
So once again you're back to saying that it provides evidence of another crime. But many people are saying the anonymity becomes a crime itself when in the context of another crime. I'm kind of bothered by that as it puts a liability (or a chilling effect, if you like) on being anonymous, something I do every day and cherish very much as an important aspect of my privacy. Even though it won't become relevant until the day I am (perhaps wrongly) accused of another crime, suddenly it will become a very huge liability if that ever happens.
Now if you say the anonymity crime is "planning and preparing to commit a crime" then that's (sort of) OK. Once again, the anonymity is part of committing a separate crime that I can at least rationalize is wrongful. But if you tell me that the pure anonymity itself is a crime then I'm very disturbed by that.
