I don't believe in IP, but I think us anti-IP types are incorrect when we claim that people who download music, movies, or software programs, wouldn't have bought the content anyway. That type of thinking is nonsense.
Are there some people who will download first and buy later? Yes. But there's also a bunch of people who would have bought a movie, album, or MMA fight, if they couldn't download it for free.
Again, I'm not pro-IP. Kinsella changed my mind on this issue years and years ago when he argued that we should only have property rights in scarce resources. Patterns of 1's and 0's are not scarce, hence no property rights. But lets not be delusional and claim that all downloaders wouldn't have paid for the service anyway.