I thought this thread was about his music. I'm out!
Isn't it fair to say that what people say and do outside of music colors the view of their music for most people?
Vrai talks of how otherwise attractive guys she might be interested in become really ugly when they open their mouth and she finds they are idiots. Jane Fonda is an otherwise gorgeous woman many can't stand the sight of because of her views. The Dixie Chicks are a pretty good country band and their career fell off, a lot, because of their politics. I thought Bon Jovi a blithering idiot until I heard of his politics. Then, I became sure. Springsteen.
If Dave Mathews roamed the earth waving the American flag, that would change a lot of views of him. Of course, it would also change the view of a lot of current fans.
Then, of course, there are plenty of people who appreciate an artist, an actor, a musician, politicians and preachers in SPITE of what they may say or do otherwise and can just enjoy their good work.
None of that is to say anyone has to like anyone based on how good they really are. Lots of sincere, earnest music fans don't like jazz or symphonic work, genres filled with amazing talent. Dave doesn't pop out 3:00 of verse, verse, chorus, verse, chorus and out.