Exactly, then if I am a denier, I can't defend myself with arguments because there is law to just prevent anyone to do any public attempt of demonstration.
But I am allowed to invite you in my private home to have a debate with you and try to explain you why I don't believe it.
Well, the core of the problem is that nobody can defend themself because the holocaust really happened. So those who'd like to defend themself are really only looking for a public platform to spread stupidity and there's no good reason that it should be allowed, because this level of stupidity is highly discriminating. Laws against hate speech are very similar in nature.