There's a Big difference & you know it.
Being a proponent of violence is a big difference from normal venting. This guy is talking about becoming a sniper or bomber. He's just one step away from the terrorists who also feel justified in killing. Is he joking? Some might like to think so, but history is filled with cases where everyone ignored the public warning signs of the mass-killer. Can anyone really afford to believe its just venting or a joke?
It's one thing to call folks bad names, it's another to star pulling a "Pat Robertson" ;-) and publicly calling for folks death.
"Rivers of blood" and "sniping" are beyond freedom of speech and have fully entered into that "unhinged" zone.