Why don't European Muslims assimilate as well as ours?

Posner argues that European labor market regulations are contributory to the threat of violent Islamism, and Becker agrees, but can't explain the seeming counterexample of the recent London bombings:

As Posner emphasizes, most immigrants, non-Muslim as well as Muslim, feel far more accepted in the United States than in Europe, are less segregated here in both their living arrangements and employment, and appear to advance more easily toward higher level jobs. As a result, they are less promising material for radical Islam, although clearly radicals are operating and planning in the United States as well as in Europe.

However, the British experience is somewhat disturbing to this thesis, for Great Britain is at least a partial counter example to our analysis. For British labor markets are very much like those in the United States; in fact, Britain has lower unemployment rates than the U.S., has equal labor market flexibility, and provides above ground jobs for Muslims and other immigrants.

I believe the main reason for the difference with the United States is that new immigrants are easily accepted in this country since it is a nation of present or past immigrants. Foreigners of all kinds have never been so welcome in Britain, and are even less welcome in continental Europe. So even under the best of economic conditions, immigrants in Europe do not easily integrate into the general society. Still I confess these vicious attacks on London subways and buses are not only awful, but I also find them difficult to understand. (italics added)

I agree with David Ignatius' understanding of the bombings as a revolt of priviledge. Bad economic policies only explain a fraction, and I suspect a rather small fraction, of violent Islamism among immigrants to the West.

It's harder to discount Becker's thesis that America is uniquely friendly to immigrants and therefore uniquely resistent to radicalization of its Muslim immigrants. I really don't know how much explanatory power this idea has. Allow me to throw out another conjecture I'm quite unsure about. Is American popular culture more socially conservative than its European counterparts, thus aiding American assimilation by being less offensive to Muslims? Is such an effect is present, then what effect has the greater presence of Christianity in American culture?

Another claim I've often read is that Europeans can't assimilate their immigrants as well as we can because they aren't as proud of their heritage. (This claim is often expressed as a condemnation of multiculturalism, not for its love of other cultures, but for its hatred of Western culture.) This claim is intuitively plausible to me, and I've read of polls showing that America is an exceptionally patriotic nation. Could it explain most of the variance between the frequency of American Muslims becoming terrorists and that of European Muslims becoming terrorists? If pressed for a quantifiable conjecture, I'd say that at least a third of the variance is so explained.

Finally, are American Muslims simply more diverse then European Muslims, and therefore less able to maintain a large, insular subculture susceptible to infection by violent radicalism? Below I present some data quantifying how American Muslims are more ethnically diverse than British Muslims. (There is also anecdotal evidence.) However, I really don't know how much this variance in diversity can explain the variance in assimilation between American and British Muslims.

Here's some results from a CAIR survey.

Mosques Grouped According to Dominant Ethnic Groups*

27% African American
28% South Asian
15% Arab
16% Mixed evenly South Asian and Arab
14% All Other Combinations

*Dominate [sic] groups are calculated by: 35-39 percent of participants in one group and all other groups less than 20%; 40-49 percent of one group and all others less than 30; 50-59 percent of one group and all others less than 40; any group over 55%. *Mixed groups calculated by two groups with at least 30 percent of participants each.

Another result is that only 24% of American mosques are 90% one ethnic group. My cursory search didn't find a comparable survey of European mosques. However, I can compare the ethnic breakdowns of American and British Muslims. America Muslims are 32% South Asian, 26% Arab, 20% African American, and 22% other (cite here; article not free online). In contrast, from here one reads that "almost three quarters" of British Muslims originate from South Asia. (More specifically, the of the Muslims counted by 2001 British Census, 687,592 were Pakistani, 261,833 were Bangladeshi, and 133,783 were Indian.)

Update: Posner also mentions that welfare benefits are more generous in Europe than in America. Mickey Kaus has also found anecdotal relations between welfare and terrorism. He concludes that "extreme anti-social terrorist ideologies (radical Islam, in particular) seem to breed in 'oppositional' cultures supported by various government welfare benefits." Welfare benefits don't exactly fall under the "labor market regulations" category that this post started out with; they're government transfers. As for their explanatory power, I'd attribute to them at least a small fraction of the variance, but I won't make a stronger conjecture because the London bombings still are much better explained in terms of Ignatius' revolt of privilege: for example, one of the bombers "had just received a red Mercedes from his dad."