My opposition to SOPA/PIPA has nothing to do with the amount of financial damage piracy causes. Whether it was billions per year or loose change from the couch, I don't like piracy in general. If you pirate, I'm not going to say anything, but I don't approve either, based strictly on the principle. I'm all for protecting the people who make the movies/songs/video games that we all enjoy, and I would never claim they don't deserve to make full profit for copies sold (yes, even if the movies/songs/games suck. It's the dark side of the free market). Large numbers of pirates contribute to the restrictive DRM that many mediums have in place today, and I think further piracy only encourages more, stricter DRM - which I believe is more damaging than any dollar amount of loss.
That having been said, SOPA/PIPA is completely the wrong answer here. It shifts the burden of proof to the owners of the websites, implying overtly creating a "guilty until proven innocent" mentality to software piracy. I think the Feds need a much more precise method of hunting down people who upload and share copyrighted material, which should be executed in such a way that the site owner is unharmed, and the Feds still have to prove the piracy in question. That would fit in so much better with our ideals here in the States. We're big on words like "freedom", "justice", etc... but unless we're willing to actually back those words up with actions, and the structure of our legal system, they are completely meaningless.