Quick outline of some problems:
- SOPA will give copyright holders power over foreign companies. If there's an organization based in a foreign country that's engaging in illegal online trafficking with citizens in the U.S., the government gets authority to barge in and try to shut it down. That's like China walking in and arresting the CEO of Apple for threatening its electronics industry.
- Third-party hosting sites are going to be absolutely screwed over. Sites like YouTube, Vimeo, and Mediafire become liable for what their users uploads, so if someone uploads a copyrighted video, guess what? They get sued. Their userbase is large enough that there's no possible way they can control everything that's posted.
- SOPA will actually hurt a great majority of businesses more than it will help. Companies will have to invest in a bigger legal department to handle lawsuits, taking away from their capacity for other ventures.
- Small businesses that can't afford a full legal department are literally screwed over before they even start. Many will likely go overseas, which will really hurt the U.S. in the long run.
- Internet privacy will be almost completely dead. The only way for an ISP to intensively check for copyright infringement is to watch its traffic, which means they'll be seeing everything you do on the Web, piracy or not.
- Domain name registration removal doesn't even work. You won't be able to type in a URL to access the website, but you'd still be able to reach it by IP. It's extremely simple, actually. I'll even teach you.
So, who does this help?
- The MPAA and RIAA, obviously, that are dedicated to fighting copyright infringement.
- Big businesses that rely on trademark and lose a lot to piracy, like Microsoft, Sony, and Adobe.
I hate to bring the Occupy Wall Street movement into this, but this is a perfect example. Heavy commercial software companies controlling politics, threatening overall economic interests for their own gain.
Some interesting links, if you want to read up on it yourself:
Stop American Censorship (Activist group. Sign a petition. Also has some nice information)
Wikipedia (I don't care if it's not 100% reliable, it's still useful, stop shouting)
Insider (BSA withdraws support for SOPA; outlines some of their concerns)
H.R. 3261 (The bill itself. Read it if you like long legal documents)