Psycho, it is extremely region-dependent, what is 'mainstream'.
And of course, there are a number of very large cities there, with a vast range of lifestyle choices, ethnicities, races, religions, etc.
I honestly don't think that can be underestimated.
My native city, for example, Houston, TX, is home to about 5m people.
You'll find some pretty big pockets where no one speaks English and the views there, the lifestyle that's accepted there, etc. are very different to what you'd find in other areas.
I mean, look at the NYC metropolitan area. That's almost an entirely different culture from the rest of the country in itself.