Americans obsession with the American flag isn’t just an example of patriotism or nationalism -- it’s an example of fetishism. Some Americans, at least, have developed a cult around their flag in which that flag is treated almost as it if had supernatural powers, and certainly as if it were more than merely a symbol of America. The flag is treated as if it were America itself -- as if it were a substitute for America, such that how you treat it were how you treat America.
Some Americans fetishism for their flag is demonstrated by a near-obsessive, ritualistic manner in which they insist it be treated. Their behavior is more consistent with how people treat religious icons; obsessions about proper folding, never letting it touch the ground, not allowing it to fly after sunset, and so forth. When people treat common objects like this, we say that they suffer from a mental imbalance -- obsessive-compulsive disorder, to be exact. When they treat religious objects like this, we simply say they are devout. The flag cult demands that its way of viewing and giving meaning to the flag take precedence over everyone else's. The flag cult demands that it get to define what the flag means, what true patriotism means, and what America is. Alternative meanings, like those expressed through defacing the flag, are denied validity.