You are attacking a strawman. I did not claim that diversity is a sufficient condition for progressive values, I did not even claim that it's a necessary condition. There are many sets of values that will go together to create a "good" society (for any subjective definition of good). For the case of the US, diversity is one of those values. It is entirely possible for a country to not have much diversity and still be a progressive country. In other words, I guess "create" in the quoted sentence should be replaced with "strongly influence".

Essentially, if you're claiming that diversity isn't one of the more defining cultural value of the US, and without it the States would be the same, then I would like to hear your reasoning.