Well, it does also need to be taken into account that America still has a 'Hispanic community' and an 'African American' community, for example, people will habitually group together with people who dress and act as they do, you can see that kind of behaviour from teenagers onwards, and not just by nationality, groups form all the time regarding musical style, favourite pastimes even make of car or whether you prefer a Harley Davidson, and each of those groups will remain a little bit 'seperate' from other groups, sort of like an Elite club.
France gets a lot of stick, one minute they are anti-semitic, the next they are anti-Islamic, when, in truth what France is, is Pro-France, who can blame them really? I don't hold with all their practices regarding immigration, but they simply use a different approach. Does it work? Time will tell, the riots recently have suggested otherwise, however, I've heard people in France saying there was far far more to that than the media were reporting.
Edit : I'm sure each of you has at some point been in one group that has a member that another group you hang around with doesn't like. If you have been in that situation, you'll know the strength of group ties and the difficulties with dealing with conflicting interests.