Imagine this. Some years in the future you have a kid who did something funny while you were watching tv, so you grab your phone/camera w/e and upload it to youtube. Inadvertently a tiny bit of "Random TV show" was included in your video, now the publishers for "Random TV show" can shut down youtube because of that.
How exactly is this going to stop piracy? The US doesn't have legal jurisdiction in every country of the world (though they sure try), so websites hosting pirated content will just move over to another server in another country (like say China) and there's absolutely nothing the US government can do about it apart from maybe DNS block it in the US (but then ip addresses work).
I said pirates are the cause of the problem. I didn't say sopa/pipa are the solution.