What ruined American society?
I'm not yet convinced it has been ruined, but it may very well be in decline. To me, the biggest contributing factor to the decline is the unwillingness of some immigrants to embrace becoming Americans. In times past, people who came to this country were eager and willing to join the culture, learn the language, celebrate the traditions, and simply become Americans in general. Over time, this has changed. Over time there has been a gradual, and now too frequent, desire for many who come to this country to be among others who share their origins. We find enclaves in almost all cities and towns populated solely by Vietnamese, Chinese, Mexicans, Guatemalans, Somalis, pick a country and you can probably find a neighborhood or "Little [ insert country name here ]." Now, while this may be fine for a weekend out or for the tourist industry, it does nothing to further the ideals that once had people calling America "the great melting pot."
I do not believe there is anywhere else on this planet where a person could find as much racial and cultural diversity as you do in the United States. The continued voluntary segregation serves no one and will ultimately lead to the ruin of a great country. How long before this practice leads to a true Balkanization of America? How long before that Balkanization results in true violence between the various regions?