First of all, I am not sure what it accomplishes to protest at the funeral of a soldier that did nothing more than serve his country. The dead soldier cannot change a thing about what he did or why he did it. It is too bad that there are people who without compassion for the grieving family.
However, to prohibit the right to protest anything...In the United States constitution, it states 'the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.'" Does this law go against the freedom to assemble? From what I can find out, they have been non-violent assemblies.
Isn't it just possible that certain soldiers died to protect this freedom?
On the other hand, I would not want to have to face God someday and explain why I had stood "peaceably" with such a hateful message on a sign, at the funeral of one of His children.