You make a good point. I didn't consider it fully enough, it seems. While I don't doubt that shouting that in a fundamentalist church can be reasonably expected to cause violence, the phrase itself is definitely not a call to commit a violent act; rather it is someone expressing themselves (albeit in a rather unusual manner).
Regardless of the circumstances, if the people then attack you they are committing a crime. Ironically, the government would never prosecute someone in that situation, even if their statement fulfilled the Brandenburg v. Ohio test. They would probably instead offer you immunity in return for being the star witness