You should't need face recognition to do this (as it seems stadiums are already successful in banning people who haven't paid from entering the venue).
Vigilance is the price of liberty, and I don't believe that that there is any reason to make that vigilance "easy" for those already more than capable of doing a reasonable job of it with means that don't create a giant liability of biometric data leaks for everyone else.
For publicly-funded venues, you may have a point. But if Bimbo's or the Warfield in San Francisco wants to ban someone and it's not for a reason prohibited by law, more power to them. Casinos have been doing this for many years, and generally speaking businesses have the right to refuse business to anyone. Make them post signs if that makes you feel better, but they should be able to ban, say, a person who attacked a patron or staff at the venue (and then was swiftly let out of jail by an activist judge).