My own post is in reply, as that interpretation of America that is being offered is an ideological one proper to an American political party. Calling America multicultural is also purely a political ideological idea, having nothing to do with actual American life, and only anything to do with partisan politics. (As I already noted in a pm.) We don't have multiple law systems (rather, much that is culturally 'okay' in most other societies is illegal and abnormal in American society - as the pedophila I mentioned earlier, okay in many cultures, but not in America - an example from my own work in law enforcement.)
A commentary on sociology is not political as it can be contested on objective scientific, rather than merely ideological, grounds. Yes, some have sought to politicize scientific issues, in this case the science of sociology in other cases science of biology or medicine, but the core issues are inherently academic and can be approached from a scientific perspective. George has simply made sociological and cultural observations, he has not taken political positions.
Oh, and we do have multiple legal systems, or did you not know that each state has its own legislature with broad authority to pass laws relative only to that particular state. We even have one state whose legal system is based on the Napoleonic Code and a system of Civil Law, which is quite different from the Common Law of the federal government. And even as far as your example of sex with a minor goes, age of consent is also subject to state law and does vary from state to state ( http://www.webistry.net/jan/consent.html
To say that there is no single American culture, but rather there are dominate regional cultures with influential subcultures (African Americans in the South, Mexican Americans in the Southwest, the French Creoles in Louisiana (are they a minority there yet?)). And many of these cultural differences are seen in or enforced through state legislation.
Furthermore, to suggest that these United States are not multi cultural is absurd, it is to deny that the Germans or Scots-Irish had any cultural influence on culture, to say nothing of other influential imigrant groups such as the French (Louisiana), African Americans, Irish, Italians, Mexicans, etc. It is also to deny that any remnant of Native American culture found its way into modern American culture, which is simply not true, Native American culture has been quite influential in the forming of western culture along with pre-mexican spanish culture (the origin of the Rodeo, for example). Our culture is a hodge podge of various cultural elements from around Europe and the Americas, with notible African and a handful of minor Asiatic influences; it is a 'melting pot' in the truest sense, all these cultures went in and a new compound entirely came out, made from the old cultures but hardly resembling them. Of course, what went into the melting pot, and accordingly what came out, differed according to the history and experiences of each region.
The only region that I believe can be said to have formed much of its own culture (beyond what would be expected from any cultural evolution) is the west, and this distinct culture came from the pioneer spirit of it's settlers and the ideals of rugged individualism and egalitarianism on which it was founded (not that there was a huge choice in the matter, the only well established peoples in the west were the Native Populations and Spanish landowners, and we wern't about to give them a privlidged position in society, so meritocracy became the order of the day).