It's a religion.
A weird civic religion like nothing that came before it.
The founding fathers are thir prophets, constitution is their holy scripture, the flag their holy icon and the anthem their hymn.
You don't just change scripture :coughamendmentscough:, you don't even read it - you get a priest to interpret it and tell you what it means in this context. You take it on faith that the things in it are infallible and eternal, even though you don't understand them or know what they are.
Look at it through the lens of civic-relgious fundamentalism, and most of America makes a horrible kind of sense.