system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why denying the Holocaust is not protected under the freedom of expression? And why denying other genocides/mass killings is not criminalized in any countries?

I'm not a denier, but this dilemma has always baffled me.
gpt
In the US, denying the Holocaust IS protected under freedom of expression.  In some other countries, even those with fairly liberal free speech policies, there is not the same blanket free speech protections as in the US, and specific forms of expression (like hate speech) can still be forbidden.