system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is Holocaust denial (and other genocide denials) a criminal act in so many countries? Why is it considered dangerous and not just idiotic?

I'm not a Holocaust denier, I'm having trouble understanding why a thought crime is punishable by law. I think there has to be a reason beyond the scale - people who advocate other nonsense are generally just ridiculed, not jailed.
gpt
Because the nations where it is considered criminal were so terribly impacted by the holocaust that the criminalization of that speech is intended to prevent any similar type of repeat acts from within that group.

Basically, the holocaust denial is uniquely damaging to the nations which ban that (or they don't have all that great freedom of speech protections) due to it's scale and direct impact.