He's basically an iconoclast; mohammedanism (among other religious and philosophical movements) teaches this.
Many folks disagree. They hold that how one treats the symbol indicates how one would treat the thing symbolized if one had the power to do so. It also indicates one's attitude toward the thing symbolized. Contemptuous treatment of the symbol (the Flag, in this instance) indicates contempt for the United States, and a willingness to maltreat the USA if one had the power to do so.
Folks have been known to hang, burn, tar-and-feather politicians 'in effigy'. Nobody mistakes the meaning of the act.