Your consent is given when you choose to pay for a ticket and attend an event there.
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).
Funny you mention San Francisco since 1015 Folsom and other places now use facial recognition to bar entry to (what I suspect are) bad actors. I suppose it was inevitable that as we allow more bad behavior through diminished societal enforcement that this would move into the private sphere. It's interesting to observe that places like San Francisco have moved into this kind of multiple-parallel-government structure.