The thing is if you are going to argue these kinds of things then surely you would have to put people in prison for believing in God who according to the Old Testament was really into genocide too. Or do you then put the people who don't believe in God in prison too as they are obviously denying Godly genocide? Either way it's a slippery slope to be locking people up for having opinions. The state is what led to Hitler, so using the state to silence freedom of speech is probably not the best way to advance anything.