Patriotism Paradox? (U.S.)?

In the United States, why is it viewed as acceptable and even patriotic to wear American flag underwear and thongs, while burning the American flag, which is a right protected by the U.S. constitution, is viewed as socially unacceptable to the point where some say it should be a crime? Is rubbing one's sweaty on an image of the American flag NOT flag desecration?