Nothing wrong with face recognition itself, when used responsibly. People who commit crimes, for example, at MSG's venues should be banned! The problem here is that they're denying service to people who have done nothing wrong. In some cases just for being associated with a law firm which is representing clients against MSG.
Suppose Google decided to ban you from using all Google services, just because you work (or once worked) for a law firm that is representing someone in a suit against Google. Would that be fair?
Imagine if you had to sue a company for a wrong doing, but still would require the services of said company. They could pressure you to drop the suit, by using this tech to deny you access to their services.
So even if the suit had merit, the company escaped being sued. So this would produce unfair outcomes.
In other words, a company discriminating against customers should be illegal, except in specific circumstances allowed by the law.
That's usually done to unruly fans. This is controversial for two reasons: the tech angle (automatic facial recognition) and that the denial of service happened to an attendee who had shown no signs of unruly behavior and only happened because of her place of employment.