Holocaust Denier Punished

Amid the chaos that has erupted throughout the world over the question of free speech, a new controversy has sprung up in the country of Austria, where British historian David Irving was arrested for publicly denying the Holocaust.
Being a liberal person, this issue has personally challenged my thoughts on ethics and freedom.
On the one hand, is David Irving an ethical man for having said that one of the greatest crimes against humanity never existed? Of course not. However, should he have the freedom to exercise his free speech? Certainly, it is a perplexing issue for a concerned individual such as myself to dissect.
Then, suddenly, like a clap of thunder, a third voice entered my head and said, ‘Wait a second. Freedom of speech is protected under the American Constitution, so why the hell do you care what Austria does to a Nazi?’ Here’s some central European country that hasn’t been heard from since, ironically, World War II (and maybe a few James Bond movies), and now you’re fretting over their laws. Austria is a different country and what they decide has nothing to do with any of our affairs.
This leads to a mistake that is made way too often these days, namely, the belief that the whole world is run by the Constitution. Freedom of speech, as we know it, is protected under the First Amendment, and is an American law, not an international one. Believe it or not, other countries have their own laws and constitutions which dictate their own rules about freedom. For instance, I can go to any other country in the world right now and get utterly shitfaced despite me not being 21 (in fact, America has the highest drinking age in the world