Because the aspects of NYC and LA that are being promoted on this thread as evidence of culture are the aspects I would define a their non-culture. As you say,

Because the aspects of NYC and LA that are being promoted on this thread as evidence of culture are the aspects I would define a their non-culture. As you say, there is a selective reinforcement of the character of the place via affinity in-migration (mostly just youth-culture btw), but to have a culture proper there must be an ethic or morality specific to that place. If you can't say "we don't do that sort of thing around here" and mean it only for that place, then there really is no culture there, imho. Growing up in NYC, my experience of neighborhoods were that they indeed had their unique cultures and it was largely a function of their unique demographics. But that sort of thing isn't what's being argued for on this thread. The happy presence of an Ethiopian restaurant here or an "authentic" Chinese restaurant there represents the values of an entirely different ethic -- one that is interchangeable whether you are in NYC or LA (or any other 1st world megalopolis). The ethic or morality of that definition of culture is entirely unspecific to place. It _is_ specific to a rootless urban managerial class (which is why that class is entirely supplantable across any of these supercities). The kind of insular cultural ethic that actually defines a "place" is anathema to these values and would be stamped out in "ethnic neighborhoods" if not for a kind of benign and patient condescension. (With the caveat that we still like to have a bit of "flavor" in the form of token representations of "other cultures".)