One has to wonder if the police would have stepped in and arrested a US citizen should they have chosen to similarly desecrate the Mexican flag at this rally. Evidently, since desecrating the American flag is a federal crime, the local and state police wouldn't arrest these "protesters" for having done so as it was not a crime within their jurisdiction. Only the feds could arrest them, and since they won't arrest illegal aliens for even being here, why should they arrest them for this "petty" crime?
Notice the toilet seat and paper sitting on the American flag? Care to bet whether such a protest in Mexico would land an illegal alien American in a Mexican prison, and justifiably so?