18 U.S. Code § 700 - Desecration of the flag of the United States; penalties
(a)
(1) Whoever knowingly mutilates, defaces, physically defiles, burns, maintains on the floor or ground, or tramples upon any flag of the United States shall be fined under this title or imprisoned for not more than one year, or both.
Enforce it. While we have freedom of speech and expression there are some items that are off limits. The United States flag is one. Make it mandatory that anyone desecrating the U.S. flag be fined $10,000, imprisoned for one year and registered as a terrorist.