Maybe my outlook is flawed, but people do believe in the book (any book) (the same as the flag) and many people have died for it. Disrespecting the book or the flag, IMO us like pissing on their graves.
A few things make us different from most animals, we often bury our dead with some sort of ceremony, we often grieve for extended periods.
It's not just respect, it is deeper than that, in most people.
Vandal is a word that pops into mind, as a label for someone who purposely messes with another's symbols. Immature at least and possibly a sign of mental illness. Many people rationalize, to support flawed behavior, another sign of immaturity.
To address another tack in this thread, Patton (paraphrase) "Your mission (duty) isn't to die for your country, but to make the other SOB die for his."