They are currently working off the idea that any unauthorized use is stealing money right out of their wallets, and they are patently wrong. Because you're right - people DO see fanart and become fans! It is absolutely free advertising, and helps build goodwill for the show AMONGST existing fans, keeping them in the fandom.

I also think you're right that most, if not all, fandoms aren't friendly to pirated DVDs and their peddlers, although I'm not really in any communities of any sort at the moment.