"Court held that government cannot punish inflammatory speech unless that speech is directed to inciting, and is likely to incite, imminent lawless action.
...In this case, the court found that Hess's words did not fall outside the limits of protected speech, in part, because his speech "amounted to nothing more than advocacy of illegal action at some indefinite future time,"[1] and therefore did not meet the imminence requirement."
From Cameron's case:
"The Methuen Chief of Police even stated: 'I do want to make clear he did not make a specific threat against the school or any particular individuals...'"
Brandenburg lays out the incitement exception to the First Amendment. If I understand the allegations correctly (and that's made more difficult by the lack of the actual lyrics) the prosecution claims that the speech would instead be unprotected under the true threat doctrine.
The leading Supreme Court case on that doctrine is Virginia v. Black 538 U.S. 343 (2003)[1], but unfortunately it's neither as clear nor quotable as Brandenburg. Here's the gist of the rule:
"'True threats' encompass those statements where the speaker means to communicate a serious expression of an intent to commit an act of unlawful violence to a particular individual or group of individuals. The speaker need not actually intend to carry out the threat. Rather, a prohibition on true threats "protect[s] individuals from the fear of violence" and "from the disruption that fear engenders," in addition to protecting people "from the possibility that the threatened violence will occur." (internal citations omitted)
"Court held that government cannot punish inflammatory speech unless that speech is directed to inciting, and is likely to incite, imminent lawless action.
...In this case, the court found that Hess's words did not fall outside the limits of protected speech, in part, because his speech "amounted to nothing more than advocacy of illegal action at some indefinite future time,"[1] and therefore did not meet the imminence requirement."
From Cameron's case: "The Methuen Chief of Police even stated: 'I do want to make clear he did not make a specific threat against the school or any particular individuals...'"
Vague threats are not illegal.