Frequent oversimplification/misintrepration; you do have the right you yell fire in a crowded theater; what you don't have is a right to do it falsely (i.e. no fire), which is, ironically enough, what whole statement/crime hinges on. What a difference a single word can make! http://en.wikipedia.org/wiki/Shouting_fire_in_a_crowded_theater
To further clarify, saying/making it illegal to yell fire in crowded theater would be prior restraint (http://en.wikipedia.org/wiki/Prior_restraint#Prior_restraint_in_the_United_States); which to paraphrase is to stop you from doing something/owning something before you do it/own it, on the basis you might do it/use it wrong. Easy example: making a law banning lawnmower ownership/possession because a person might use one to brutally attack a playground full of schoolchildren would be an illegal law.
IOW: you can't tell a lie causes lots of people to kill/injure one another unnecessarily. Along the lines of slander or libel - it's not illegal to say something damaging to a person or company, it is illegal to do so when that statement is factually incorrect. IOW: the truth is its own best defense.
While I would agree with you that on a societal level that a funeral is a semi-private event and WBC protests are at best in very poor taste, AFAIK, from a legal and practical perspective most funerals are held in at least a semi-public public place outdoors with limited or even nonexistent restricted access; making them in practice a semi-public event.
I think of a lot of people misunderstand the 1A; from my studies how it seems to be intended is, "this is a completely gov't (fed, state, local) hands-off topic, not open for debate." No addt'l laws respecting or denying the 1A, one way or the other. Let things sort themselves out - but without violence, one way or the other (which is all the law is, by definition - situations that gov't-sanctioned violence has been deemed OK).
The problem is when people don't and convince themselves that one exception to the 1A is OK is extreme circumstances, then two, then three; next thing you know, another fundamental right has ceased to exist in practice, and we have yet another limited, revocable privilege managed by an inept, top-heavy bureaucracy made up of "leaders" unfit to run their own lives, let alone direct the lives of over a quarter billion people.
"Somehow the notion of unalienable liberty got lost. It's really become a question of what liberties will the state assign to individuals or rather, what liberties we will have the strength to cling to." Paul Denton
