Instead of "best" and "not best" cultures, how about "acceptable" and "not acceptable" cultures?
If a culture's practices are not acceptable to us, then we have every right to use military power to force them to change.
If we can live with their practices, then yes, diversity is fine and I have no objection to it.
As an example, take Italy. What if, at the very beginning of the Amanda Knox case, we invaded Italy, killed every judge in the country, killed everyone who tried to resist us, rescued Amanda and Raffaele, and went home?
That would have been a far better course of action than what we did do. And I bet the next time some third-world hellhole thought about illegally holding an American student in prison for four years, they'd think twice.
Our national motto should be: Speak softly, carry a big stick, and clobber the hell out of anyone who messes with us.