Yeagh but my point was that the book I gave the link too claims people who "actually practice" a religion tend to marry within that religion. It claims that 90% of practicing Church of Scotland people marry other members of the Kirk. Then I imagine a proportion of the remaining 10% will marry other Christians or people who are just nominally Christians. If practicing Moslems tend to marry other Moslems then they are just doing the same as the wider non-Moslem religious communities. They are no different so it makes no sense to single them out. And you don't need to marry a non-Moslem to integrate anyway!