The "fire in a crowded theater" analogy is from Schenck v. United States[1], in which Justice Oliver Wendell Holmes Jr sent socialists to prison for distributing flyers that protested the draft in World War I. So yes I am against more restrictions on speech. Any restriction will be abused by those in power. The cure is worse than the disease.
But all that demonstrates is that even with the strong free speech protections guaranteed by the constitution, if the government wants to shut down particular behaviour it will find a way. FWIW I agree that prison is an unreasonable way to handle distribution of flyers protesting against a law, but I wouldn't have an issue with them simply being removed from public places, which might have been the result if the government had more freedom of choice on when censorship was justifiable.
1. https://en.wikipedia.org/wiki/Schenck_v._United_States