If a frustrated user repeatedly sent me threats of physical violence packaged in a complaint letter, I'd turn it over to the police in a heartbeat. That's absolutely not a helpfully frustrated user, that's a real threat. This behavior is not just socially unacceptable, it's so unacceptable that there are longstanding legal structures in place that make it illegal. There are no distinctions between virtual and physical here, it's a real person communicating a threat to another real person using a digital medium instead of a physical one. Filming yourself committing a crime in digital format vs. physical tape/film is basically the same idea. "It's just bits" doesn't hold water or we'd not have most of the internet child porn laws, or most of the copyright and patent law cases going on, none of the internet censorship laws, Wikileaks wouldn't feel threatened, etc.

People are routinely arrested and convicted for basically the same type of behavior directed at public officials spawned from aggravations and frustrations of similar sources..."bugs" in laws, perceived unfairness, disagreements on important decisions, racism, xenophobia, etc, etc, etc (I suspect enforcement is greater in this situation because public officials tend to know the law and exercise their rights against this behavior more often).