That's not exactly true.
"Speech is not protected by the First Amendment if the speaker intends to incite a violation of the law that is both imminent and likely."
Someone randomly spouting off that people of a race or ideology should be wiped out doesn't always/exactly pass this legal test.
Great point. Visit any US neo-Nazi website and you’ll see language that one could argue is “threatening to a specific group”. But unless it’s “hey, everyone gather at 5 pm on Main St so we can start shooting people”, it’s still protected language.
That's actually a point that I don't think has been decided yet, specifically "imminent". It's been ruled that "at some unspecified point in the future" doesn't count, but I can't find a case (with an admittedly short search) about where the exact boundaries are.
I don't know what the exact legal definition of imminent is, but the layman's definition involves the thing happening soon.
It may well depend on how close to 5 it is (but what timezone?).
The same sentence with the words "right now" would almost certainly meet the test though (assuming the action was actually likely to occur).
Someone randomly spouting off that people of a race or ideology should be wiped out doesn't always/exactly pass this legal test.