I thought we were talking about speech? With "threatening to harm people" were you thinking of a physical motion like the thumb across the throat kind of thing? And if Brandenburg doesn't apply, I've gotta think there's an equivalent for it.
https://www.law.cornell.edu/wex/brandenburg_test
The Brandenburg test was established in Brandenburg v. Ohio, 395 US 444 (1969),
to determine when inflammatory speech intending to advocate illegal action can be restricted. In the case, a KKK leader gave a speech at a rally to his fellow Klansmen, and after listing a number of derogatory racial slurs, he then said that "it's possible that there might have to be some revengeance [sic] taken." The test determined that the government may prohibit speech advocating the use of force or crime if the speech satisfies both elements of the two-part test:
The speech is “directed to inciting or producing imminent lawless action,” AND
The speech is “likely to incite or produce such action.”
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So I'd say you're wrong in this case, but you're just as good a lawyer as I am