The psychological impact of wearing a mask cannot be under-stated. Without their masks, it's doubtful that there would even be an "Antifa".
It's very telling of the inherent mentality that they are willing to role-play the 1930's as long as they retain their anonymity, but are not comfortable with having their views outed in public to avoid embarrassment in the eyes of their families, relatives, friends and (unlikely) co-workers. It's almost an admission of guilt, that what they are doing is not really something that is to be taken seriously.
If you seriously believed in what you're doing, instead of believing, atleast subconsciously, that it's just a "phase", a way to get some kicks out of doing something reckless, then you'd be content with putting your face out there.
Right now, it just seems that the Antifa are like a group of kids on a playground, who don't want anyone interfering with their little game.