I don't think it's a good idea. Too many unresolved issue. One thing is what defines a flag.
Why doesn't some "inventive" local authority or prosecutor go after flag burners using the same laws that are used to prosecute cross burners. Why is the speech of bigots and racists limited, but not American hating lefties? It would seem to me that a case could be made for prosection using the same "civil rights" laws.