>where is it illegal to say or think the Holocaust didn't happen?
Different countries have different versions of history. Poland and Russia both claim to know a lot about what happened in WW2. The gov'ts of both countries claim the right to punish people who say annoying things about WW2. There is no clear definition of "annoying." Also gov'ts claim to operate by laws, but they always put themselves and their cronies above the laws, so nothing is really legal or illegal – it's just a question of which gangster wants to punish you.