So, what was the egregious offense, endangering all of society by words alone, uttered by by Schenck? This "yelling fire in a crowded theater"? Charles Schenck was a member of the local Socialist party, and was distributing fliers urging draft age men to oppose the draft (for World War 1) on the grounds that it entailed involuntary servitude, outlawed by the 13th amendment.
So there's your "yelling fire in a crowded theater" when you concede your right of free speech to the government.
[1] - https://en.wikipedia.org/wiki/Schenck_v._United_States