All censorship is bad?
Death threats, shouting fire in a crowded theatre, child porn?
Beyond that, protecting the freedom of speech of the likes of Nazis, who would use that freedom to harass and intimidate, consolidate power, then take away all freedoms, and commit a string of genocides is anti-freedom.
It's the paradox of tolerance - this shit is a social contract - you get freedoms on the condition you don't fuck with the freedoms of others.