I think this is splitting hairs. A conference organizer has basically one consideration: make things run smoothly. The whole effort is already so complex and error-prone that most of the time you're killing yourself just to make them work at all. Principles are nice, but when it comes down to either banning a couple people, or facing a backlash from the attendees and sponsors, that's probably the simplest choice the organizer has for the entire event. You lose two ticket sales, but the event keeps running.