Dave, while Linda Ronstadt is not in the same catagory as Baez or Phillips, she has been known to share her views. I heard her on a local talk show with a host who is known for his conservative views (Mark DeSimone).   He was expecting to chat about her latest album on a Saturday morning show that he does, and she turned the conversation around to politics. I am not a fan of his views, but I do admire DeSimone for the way he handled it - he avoided the discussion and switched her back to music.

Unless you book an artist and make them sign an agreement (or loyalty oath?)that says what they can or cannot say, you are open for anything. It is the promoters perogative to not invite the artist back again.