Most people are fleeing actual war these days. And before that it was mostly for economic reasons, not religious ones. Real religiously persecuted refugees are a rarity.

Sometimes the first generation of immigrants is more relgiously tolerant and grateful than the second or later generations.

The later generations often become more religious and zealous than the first, because they start to feel alienated and don't feel accepted in the new society even though they've grown up there and have assimilated as best they can.

Through various factors the immigrants become ghettoized and have a greater influence among themselves in their local communities; they don't need to learn the language of the home country, nor do they feel the need to assimilate to get by or even thrive anymore. They don't think they would have a chance if they did anyway, so why bother?

Bigotry from within the group against the home country's original citizens and racism against the immigrants spiral up and feed off each other, thus separating the two groups even more.

Most of these immigrant "foreigners" are actual passport-holding citizens by now and want to protect themselves against real and perceived threats.

One of the threats is how the police treat them differently than white citizens, because any one of them could be an illegal alien or a terrorist. They are more often perceived by the police to be criminals, thus furthering the divide between the two groups.

They think sharia law would be more fair, because local immigrants who understand the situation better would deal with the problem and there would be less threat of injustice from outside and prison sentences.

The immigrants feel it is their right to follow their religion, but I think that many of them become similar to the Westboro Baptist Church in their zeal. This then becomes a real problem for the home country.