I think it's true that there are midwestern cultures and western cultures -- different aspects of people that are shaped by ties that bind them in certain ways. But the reason we don't usually think of "white" culture, per se, is because it's just not something that seperates us from a majority -- and that is what tends to bind people together.
This is a reason there's such a thing as a Jewish culture, gay culture, black culture, but not really a white culture.
And let's remember that there really is an "American" culture, to which we all belong to some degree -- black, white, gay, straight, muslim, buddhist, or christian, Americans fit into a culture that is quite seperate from that of most people in the world.
Whether the OP was a troll or not, I was astounded by a few of the really racist posts by the way. In the light of those posts, I'm not sure it matters who started the thread.