No, you're misunderstanding Brandenburg.

Yelling fire in a crowded theater is not about causing lawless action; the people fleeing in panic are behaving lawfully. The act of yelling "fire" is outlawed because that panic can result in grave bodily harm to others, and is a foreseeable result of doing so.

Brandenburg deals with inflammatory speech (usually hate speech but also includes seditious speech), which must rise to the level of incitement to be criminal, specifically meaning that you must incite others to actually hurt a third party or to actually take seditious actions against the government. Otherwise, the inflammatory speech is justy the expression of personal opinion, which is directly protected by the 1st Amendment.

Not sure if you're kidding, cynical, or serious.

The entire framework of the US government's core documents and the non-legal documents written by the founders around the same time completely support the notion that these documents have purposes, chief among which is the defense of citizens from the government itself.

So, ironically, the "fire in a theater" phrase actually indicates the government can simply ignore their own laws any time they feel like it, as they did when the phrase was uttered.