The whole point of multiculturalism is that all the different groups living in a society are NOT a collective. That's why ethnic, racial & religious diversity is a weakness, because by definition, it means division. Would you like me give you a list of all the different wars that have taken place throughout history between different tribes, ethnicities, religious groups, nations, kingdoms & empires? Robert Putnam, who is the definition of a self-hating white leftist, found out when he studied ethnic & religious diversity, the serious problems it causes in society. He set out to prove the total opposite because he was convinced that diversity only had positives to offer, but after he discovered the opposite, he was so upset by it he sat on his findings for many years because he didn't want to release them to the public. Diverse societies have a total lack of trust (between all the different groups), and day to day life just becomes one big pressure cooker. Worst case scenario, it results in civil war. The best you can hope for is just tensions that never boil over, but who the hell wants to live in such a society where you constantly feel on edge, because of the lack of trust between all the different ethnic & religious groups?
As for Muslims being a part of "our societies"... no, they're not. They're the biggest offender when it comes to rejecting Western culture. They don't want a part of it and they make that very clear in every Western country they're in (and in the non-Western world, too).
Muslims believe their religion is superior to ALL other religions and cultures and they're not willing to give an inch on this. No sane person wants to invite such people into their society.