There’s a difference between expressing an idea and making a speech act. Harmful speech acts, including “true threats” in the legal sense (e.g. credible threats of imminent harm, as opposed to expressions of support for policies that would be harmful) and all the other things that you mention* may be regulated without impinging on the free exchange of ideas (although one must watch out for attempts to suppress ideas by claiming that they’re speech acts).

I’m not talking about a mob of fascists threatening to attack someone there and then (illegal) or actually attacking (illegal, and cause for justified violence in self-defense). I’m talking about a peaceful march of fascists carrying signs expressing support for national socialism. They get to march.

*I do find it odd that simply possessing images of children being raped is illegal whereas possessing images of, for example, children being murdered is not (even if those images of murder also used for the purpose of sexual gratification).