This is inaccurate. Brandenburg v. Ohio explicitly states the opposite.
Justice Douglas specifically talks about the "fire in a crowded theater" issue being one of the few types of language that is specifically illegal beginning on the bottom of page 456 below. It's a PDF file of the original decision.
"The example usually given by those who would punish
speech is the case of one who falsely shouts fire in a
crowded theatre.
This is, however, a classic case where speech is brigaded
with action. See Speiser v. Randall, 357 U. S. 513, 536-
537 (DOUGLAS, J., concurring). They are indeed insep-
arable and a prosecution can be launched for the overt
acts actually caused. Apart from rare instances of that
kind, speech is, I think, immune from prosecution. "
Justice Douglas specifically talks about the "fire in a crowded theater" issue being one of the few types of language that is specifically illegal beginning on the bottom of page 456 below. It's a PDF file of the original decision.
"The example usually given by those who would punish speech is the case of one who falsely shouts fire in a crowded theatre.
This is, however, a classic case where speech is brigaded with action. See Speiser v. Randall, 357 U. S. 513, 536- 537 (DOUGLAS, J., concurring). They are indeed insep- arable and a prosecution can be launched for the overt acts actually caused. Apart from rare instances of that kind, speech is, I think, immune from prosecution. "
https://tile.loc.gov/storage-services/service/ll/usrep/usrep...