In my experience it's pretty common for the most obnoxious, most likely to throw a tantrum person to be catered to over reasonable people.
The people who leave the book club because of Obnoxious Guy's behaviour do so quietly. They might grumble to friends, but they don't cause a scene. If they try to ban Obnoxious Guy, there' s a good chance there will be a scene - some combination of temper tantrum, vandalism, threats, bad publicity, complaints to managers (or the board, or the press), all playing the victim to the hilt. The management, naturally, doesn't want to deal with that, so they placate Obnoxious Guy, either by not challenging him in the first place, or by caving in and backing him against the staff who has to deal with him on a day-to-day basis.