It sounds like you're proposing something akin to cultural relativism. The foundations of American democracy are definitively not in cultural relativism, but in cultural absolutism:

"All mean are created equal, etc etc".

Now, we've often failed to live up to those words in the past, but it's an (ideally) constantly-improving process. Regardless, it's much, much more desirable than some anarchical cultural relativism where everyone does what they damn well please.