Negative Player Attitudes
Yes, the TO can deny entry to anyone, without stating a reason; there is always the chance that Wizards Customer Service will hear about it, and want to discuss the matter with the TO.
Also, the Store Owner (if it's a different person) can refuse service to anyone - local laws apply, of course, but Wizards Organized Play recognizes stores' and organizers' need to manage their events and protect their own interests.
As a judge, I'd recommend that you and the TO talk to the player at the start, and ask him if he has any concerns he'd like to share with you about the event. Give him a chance to explain his concerns - that alone may defuse the whole situation. If he doesn't express any concerns to the TO at that point, but starts complaining later - then you and/or the TO can certainly ask him to stop (as a direct instruction from a tournament official), and apply USC as appropriate from there.
I recommend trying to avoid the whole situation: either give him the chance to discuss his concerns at the start, or - if you're quite sure that won't help, and he'll try to cause trouble - just deny him the opportunity by refusing him entry. (Doing that will almost certainly lead to all sorts of social media attacks, etc.)
Thanks - Scott Marshall, L5, NetRep