I understand what they are doing, and you are right some groups are very friendly to work with. But why would you even consider going into the student lot at a tailgate and be highly vocal and overly pushy.
I've seen it a few times.... the only reason for that behavior that I can come up with is that some people are just A-holes who believe it is their duty to tell everyone else how to live their lives.
The worst folks I have ever seen were the ones standing outside the stadium yelling at everyone 3 or 4 years back. Telling everyone they were going to burn in hell for the "sin" of drinking a few colds ones and watching a football game on a Saturday. I almost punched one guy after he called my friends' wife a ***** without any provocation, which of course is just what he wanted.