A piece of cloth, however symbolic, cannot be compared with a stone monument that is unique, artistic and highly valued as art as well as representation. Therefore, defacing property like that, which has intrisic value as belongs to some authority, has to be considered a crime. That is not true of any flag, esp. one bought for the purpose of protest. Actually, I think the protesters show the significance of a flag in burning it, that it MEANS something, like the tricolor or the Cap of Liberty.
Flags are easy to replace; monuments like the Afaghani Buddha and Mt Rushmore are not. You cannot equate the two. But if someone tampered with a flag over a govt building, then the govt would have a property issue.
Also, again, proper etiquette was to BURN worn flags, vs. putting them in the garbage, meaning the act of burning wasn't the issue but the context of said act was. That is (symbolic) SPEECH, which I believe is why flag burners are using a protected right of remonstrance and it would be govt tyrany to legislate otherwise.
Of course, had the colonists known how much having one's own federal (or central) govt would cost, they might have just kept the king. It was CHEAPER than actually paying for those forts, troops and whatnot. The British population actually was far overtaxed vs. the Americans for having said colonies (13:1 ratio) and actually the Brits benefitted greatly from losing that burden.
Dante non ha mai immaginato questo cerchio dell'inferno!