First let me say that I don't like the idea of public domain to being with. I'll never understand why Someone like Grahame-Smith can put his name next to Jane Austen on her book just because we past a date and he added to few lines to it is crazy. I don't know if Austen's estate is still around or not but the idea that Grahame-Smith could get paid for something that he didn't write is nuts and 80% of that book is the original Pride and Prejudice. Yes, it's legal but just because it's legal doesn't make it right.
While DS is dervative of many classic works I've yet to see his name appear next to Stoker or Shelley. Most stories are dervative of some other story. Most writers are inspired by what others write. That's very different from taken a finished book, changing it and adding your name to the front cover.
I'm ok with DCP, JP, or whom ever stopping people from writing fan fiction, fan films, t-shirts, or whatever they want. I do think they should keep in mind that without the fans they would be making this new film or having fest. Yes, they need to pay bills and eat, no one is says that they don't need to. I just think that if the fans feel like they are being taken advantage of that it won't be good for anyone, fans or anyone.