Blowing up a building can be expressive speech, urinating in public can be a political statement. To burn an object is to demonstrate one's contempt for it, not speech. It is the antithesis of speech. It is not a form of argument. It is an act of contempt for the very idea of reasoned argument.
Flag burning is no more speech than a child's temper tantrum.
And to suggest that the Founders and Framers intended to protect such public displays of childish pique, to suggest that this is what the first amendment free speech clause protects is demeaning and it is degrading. Free speech has never been absolute as our laws against libel, slander, copyright infringement, and so many more prove. By freedom of speech the Founders meant the freedom to make reasoned arguments about matters touching the common good. They did not mean a freestanding right to say anything on wants, any time and any place. Freedom of speech is a freedom inherent in the dignity of the people, and the Government should honor it and protect it so that democracy might flourish.