Commonly understood as a "crazy" message, no doubt. But is it protected under the 1st Amendment?
It has been said that hard facts make bad law, and that definitely fits here. On one hand, you have the need to protect the ability of those resting (and their families) to rest in peace. On the other, there's the need to protect one of the freedoms our soldiers die(d) to protect - freedom of speech.
Justice Holmes once said that "even the most expansive interpretation of the 1st Amendment does not permit one to run into a crowded theater and falsely shout 'fire'." - his way of saying that no right, not even the 1st Amendment, is absolute. However, Justice Brennan effectively countered saying (paraphrase) "a core principle of the 1st Amendment is simply because a large portion of society finds certain language 'offensive' does not mean it should be prohibited" - his way of saying the 1st Amendment should closely guarded.
The opposition to these funeral protests are content based - which is subject to a strict scrutiny standard (rarely trumps the right of freedom of expression guaranteed in the 1st Amendment). Further, the opposition likely fails the time/place/manner test because these protests occur at a distance (sometimes miles away from the actual funeral). By jurisprudential standards, there is no real threat of incitement, fighting words, trespassing, violation of noise ordinances, etc. These protests are conducted in a way which allow expression of their message (however whacky society may deem it to be) while still allowing for a peaceful (at least on-site) funeral ceremony to be conducted.
So, how do we honor our troops best (assuming that is the right question to ask)? By protecting one of the core freedoms for which they died defending? Or by quieting these protests as being disrespectful of their service?