Brad Plumer has a great overview of SOPA and PIPA and why they’re so dangerous. Here’s one reason:
The bills allow sites to be taken down without legal oversight. As Public Knowledge has pointed out, one little-noticed provision in both PIPA and SOPA would grant Internet service providers broad immunity if they voluntarily block perfectly innocent users or Web sites from the Internet. Copyright holders like the movie and record industries could draw up sweeping lists of sites they didn’t like (even sites that should be protected under fair use) and pressure Internet service providers to take action. As long as the providers could claim they were acting “in good faith,” those sites and users could be blocked without any oversight by the courts — all because Hollywood was feeling a bit vindictive.