This is the problem with thought experiments regarding crime: they always make the facts 100% certain, when in real life, the facts are never 100% certain. If we were to rephrase your thought experiment, it would be:
"Some guy said some other guy was going to kill him. Let's throw that some other guy in prison for a while, just in case."
Not quite as clear-cut as you think, is it?
Weev did literally threaten to murder Kathy Sierra, and he then bragged about doing so on multiple public websites. So, yes, it is quite clear-cut.
(And, please, at least think for a minute before you try to rebut by saying that he didn't mean it, so it shouldn't count.)
Give it up, man. The guy whose image you're trying to clean prefers it nice and dirty.
Regardless of whether you truly intend to carry out the threat, the threat itself is a form of violence. It imposes your will on an unwilling subject.
If you rob a bank with an unloaded gun, you can't claim afterwards, "oh, they were perfectly safe and didn't actually have to give me the money, so therefore it wasn't a crime."
If I were to threaten to murder you, you wouldn't expect the police to say "Eh, nothing we can do, he's got a right to free speech. Call us back after he shoots you, you'll have a case then."