I believe the ticket stub says something like they reserve the right to refuse service. They can ban fans who get caught throwing bottles or fighting in the stands.
A ban based upon the “right to service” for fighting in a previous arena - that I can see.
But how can someone be banned for being a racist?
What next, banned for being an adulterer, an alcoholic, an ex-con, someone covered in tattoos that the NBA doesn’t like, and so on?
How many sins can one be banned for?