And to be crystal clear here, at least in the US.
threats of violence, up to and including death threats, are completely legal.
What's not legal is threats of violence with both the intent and the means to follow through.
If an 80 year old man walks up to and tells me they're going to kick the shit out of me, it's perfectly legal. Not only is it legal, no one is going to do anything about it until that man actually attacks me.
If The Rock walks up to me and tells me he's going to kick the shit out of me, it's very clearly illegal (assuming we know intent, of course) and he will go to jail for it.
This is why things like repeating can also be illegal. If you never have the intent or the means to follow through with a threat, but do it repeatedly to affect mental state, that too is illegal for a different reason.
But the presumption that this speech is de facto not legal is absolutely incorrect, in the US at least.
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Libel is not criminal in any way, shape, or form, and is a bad example as a result.