Why is the blackout happening?
Wikipedians have chosen to black out the English Wikipedia for the first time ever, because we are concerned that SOPA and PIPA will severely inhibit people's access to online information. This is not a problem that will solely affect people in the United States: it will affect everyone around the world.
Why? SOPA and PIPA are badly drafted legislation that won't be effective at their stated goal (to stop copyright infringement), and will cause serious damage to the free and open Internet. They put the burden on website owners to police user-contributed material and call for the unnecessary blocking of entire sites. Small sites won't have sufficient resources to defend themselves. Big media companies may seek to cut off funding sources for their foreign competitors, even if copyright isn't being infringed. Foreign sites will be blacklisted, which means they won't show up in major search engines. And, SOPA and PIPA build a framework for future restrictions and suppression.