Christopher Columbus discovered America. We all know that. We know it because we were taught that in school. Our parents were taught it, and their parents, and most likely, our children are being taught that as well, so it must be right, right?
Long before Columbus, before Leif Erickson and the Vikings, there were people living here, indigenous people who had built great civilizations, such as the Mayans, and yet, in our Euro-centric education system, those people are not credited with their discovery.
Suppose you began to question this idea. You set up a Facebook page dedicated to questioning the truth, but some people urge the owners of Facebook to remove your group from it's site. What's the big deal? It's not like you put up a page dedicated to killing all native Americans or anything. And yet, although you are not harming anyone with your belief system, you are guilty of a "thought crime" because your ideas, as ludicrous as they may be to some, and repellent to others, they are mere thoughts, that, right or wrong, sane or bull goose fucking looney, are your thoughts.
Once they can make one idea, an intangible thought a crime, then they can start adding more. Lots of people believe things that are wrong in my opinion, Christianity, Elvis is alive, the moon landings were faked, or that American Idol is the best show in the history of television. Yet, No one Demands these thoughts become hate crimes. I certainly don't. In this crazy mixed up world, people certainly have the right to believe what they will, because, they're really not hurting anyone but their own credibility.
Columbus never set out to discover America, he was merely seeking a new trade route to India by proving the world is round. He was half successful. But even with revisionist history, people will believe what they want to, in the face of undeniable facts. There are still people who believe the world is flat after all.