So the guy is an idiot. But he should have the freedom to express his views - even if they are demonstrably wrong.
Unfortunately, too many Western countries have outlawed some very specific forms of speech and prohibitted some from expressing their views. If they can take those rights, they can take your rights, too.
Having laws prohibiting expression temporarily pushes the issue under the carpet. Austria may be better off with a better-educated public that could specifically refute the platform used by such hate mongers.
I wonder though ... It feels like there is an underlying issue that is not getting addressed. What is it about this holocaust-denial message that makes it so persistant?