It actually is illegal in a fair amount of jurisdictions, and depending if your fascism includes calling for imminent lawless action, as fascism quite often does, it may not even be protected in the United States.

That’s kind of like saying being a jerk is illegal if it means you’re calling for something illegal while you do it.

Where did you check though? Because there are multiple places on Earth where it is actually illegal to promote fascist rhetoric and talking points.

When prosecutors, police and lawyers agree with them(or can be pressured), legality means nothing.

Don’t forget the ideological attorney generals.