I can't speak for Europe -- but for some reason, NYC is able to largely absorb and intergrate them just as it's been absorbing and intergreating immigrants for three hundred years or more. That's not to say there aren't lunatics out there.
However, what is interesting, of course, is that NYC has very large populations of both Jews and Muslims compacted into a relatively small geographic area and there is no fighting in the street...
for 267 "no fighting in the streets" no, not yet... however...
we also have 40,000 police.
and after 9-11, the mosques and islamic centers were some of the places where those police were heavily deployed. absent that, there would have been incidents at those locations. and the media covered up alot of the real "street reaction" in these communities after 9-11.