Not exactly. The Supreme Court has ruled that general hateful statements can be protected, but if a politician says "Democrats/Republicans should be exterminated" in a way that sounds like a real threat or call to action, it can become incitement or a true threat. So the line isn't about the words alone, it's about context and intent.
The standard as decided in Brandenburg v. Ohio is "imminent lawless action". You're correct that context matters; the speech must be tied to an imminent violation of law. This is a very high bar and in practice is very hard to reach.
Yes the US laws aren't prosecuting speech in isolation, it's always involves some sort of IRL plan to do something illegal. Just like criminal conspiracy laws, they aren't just about telling someone you plan to commit a crime but actually taking earnest steps towards a crime with another party.
If police have QI to stop your speech with impunity, and actually do so, that is just regulating that speech with extra steps.
>The case you cite doesn't appear to make your point.
It does if you go on and read the judgement, which cites that that it is reasonable to initiate a stop for obscenity, which was part of the reasoning used to grant QI.