Mostly it has to do with a very well known issue with many Muslims, which is that they don't want to assimilate to their new cultures, or even respect that they are different. I know many Muslims are quite capable of perfectly coexisting with others in the west. However, personally, I have experienced quite a few instances of them being critical or disdainful of the customs of their new country. It makes you wonder why in the first place did they want to come, and in such cases you realize they don't want to come live with us, but come and replace us who think differently. It's sad, but it is a reality. And it will of course generate distrust of the whole community.