What legal grounds is there for a lawsuit?
None, and thats why these types of freepers resort to silly boycotts of publishers or television shows - whatever has struck their fancy this week.
The version of "Free Speech" they speak of is odd to me. They claim everyone has a right, which is fine. They claim that the right does not include the right to a "forum" or to force someone to publish their work. I agree, and that's fine. But, what they try to do is petition every possible distribution source to get them to deny publication or whatnot. They go after sponsors, web hosting services and even try to get zoning boards to stop the production altogether. Kind of scary sometimes if you ask me. Its kind of like, "Yeh, you have the right, but we will try everything possible to make it impossible for you to excercise your right".
I'm not a lawyer - but any law that could apply should be used.