Flag worship as superstition.
Under the law a flag which becomes dirty or torn is to be buried or cremated, that is, treated as a living thing imbued with spirit. Which is to say, as a totem.
The psychology is surprisingly straightforward. The ostensible religious views defended by many on the right outlaw idolatry, among other forms of superstition. Yet these people are superstitious to the depth of their bones. Under pressure of religious repression their superstition becomes displaced onto a new object, like toothpaste flying sideways from a tube smashed by boots. The flag is convenient because socially sanctioned, reinforced by state encouragement and, where necessary, force.
The tattered flags which flutter from car radio antennae are actually illegal. In former eras of patriotism it would have been considered gravely offensive to allow the flag to become desecrated in that way. It's significant that nowadays nobody arrests the drivers.