And I get the "slippery slope" argument, especially regarding freedom of speech. All dictatorial regimes have used censorship and propaganda as methods to control their citizens. But lets keep our perspective and stay with this one example rather than entertaining all hypothetical situations.
The Austrians have the right to decide this for themselves. If the Austrians want to jail Irving for what they consider to be inciteful speech or hate speech, then it is their right. Even we place limitations on the freedom of expression. My only hope is that we limit freedom of speech on a case by case basis and for reasons more substantial than just not liking what someone has to say.
You can't slander. You can't scream "FIRE" in a crowded theater. You can't lie in advertising. All violations of freedom of speech. That the holocaust happened is an objective FACT. That it was pure evil is a subjective opinion. To me, lying is a greater offense than having an opinion I find offensive. In all but extreme situations, we are free to have and express offensive opinions, but not to lie about facts.