That link seems suspect to me. India is rife with crime.
Daily life, even for rich people, involves lots of activities that would be crimes in a Western country, particularly official corruption.
Anyway, you spoke in terms of "criminality in some American cultures", which sounds like a euphemism, since you neglected to name them. Although you followed it up with your hetereogenity thesis I (like many readers) was already lost.
I do agree that it is the rifts between groups that ultimately cause all the problems. However, who's really to blame for that? America's slave-descended population have been in the country for over 500 years. By any normal expectations, their original culture should have been completely blended with the mainstream culture hundreds of years ago. And a large extent this is true of those blacks that enter the middle class and beyond. But for those that are trapped in a ghetto lifestyle -- with ghetto attitudes -- I don't think you can attribute that up to cultural differences. That's circular reasoning again. Something else is keeping the cultures separate.
I think we should be open to the idea that the forces keeping the cultures separate are both external and internal to the black community in America. Still, anecdotally speaking, as a Canadian I find the racism in America to be pretty breathtaking. White Americans, whether liberal or conservative, take it as a given that there's always some part of the city dominated by blacks where gunfire is heard at night and the cops are afraid to go. If you probe even a little bit you find that most white Americans, even nominally liberal ones, think blacks have lower capacities than they do. This seems to me, with my Canadian attitudes, like a shocking abandonment of a large part of your citizenry.
In any case, heterogenity doesn't always lead to a higher crime rate. Toronto is over 38% immigrant [1] and yet has a low crime rate. Montreal has been riven by cultural heterogenity (between English, French, and others) ever since the 1700s, and yet has an even lower crime rate. [2] I'm not saying Canada is perfect in this regard, and it is a pretty universal rule that the newest immigrant population has a higher rate of crime and organized crime. But, unscientifically, it seems to me that the availability of better social services, less inequality, more equitable law enforcement, plus a very strong tradition that the norm of "Canadian" isn't any particular race [3], must all be factors in mitigating this.
[1] http://www.mta.ca/about_canada/multi/
[2] http://www.toronto.ca/quality_of_life/safety.htm
[3] Even the gangs in Canada are sometimes multiracial: the "United Nations" gang is famous for this. http://www.vancouversun.com/Gallery+gang/1350012/story.html