This is an element of Bush-era Republican politics that I just don't get - freezing people out of campaign events because they aren't supporters.
I understand if you're very worried about protesters you want to be extra careful, and I also understand that you don't want your opponents' signs or apparel at your event. But when you're having an event at, say, Penn State, and the President of the university is a "big Democrat," the longstanding norm is that what you do is have him up on stage to wave at the crowd and then you make a little quip about how he's a Democrat but he's OK and he smiles and he leaves and yuk yuk yuk. The chances that the Penn State prez is going to scream "war criminal" or do anything to disrupt the event is just vanishingly remote.
The fact that McCain, and particularly Palin, are unable to bring themselves to observe these sorts of niceties suggests something very troubling and unstatespersonlike about their temperaments.