NYC is a melting pot of multiculturalism. There are many different neighborhoods, in which people practice their own individual cultures and/or religions. Jewish people go to Temple, Christians go to Church. Heck, there is even a Buddhist temple not too far from my home.
This is the thing: People can practice their own culture and/or religion, while still being connected to a larger culture. People can attend their place of worship, cook their native food in their own home, hang out with their own kind, etc. However, when they leave their home and interact among people of different cultures, races, or religion, they have the ability to then adapt to that norm. People often have multiple selves.
Its implausible to assume there will be one uniting culture. People will practice their religion/culture in their own homes and places of worship. However, as stated above, most will adapt when they leave their home. Thus, you can have multiculturalism, as long as people are going to respect other cultures when they leave their homes or places of worship. In my neighborhood, its never been a problem. As stated, there is almost zero crime.
Perfect example: A friend of mine is Indian. He attend a predominantly Indian place of worship, eats Indian food, prays to his Indian Gods, and celebrates many traditions associated with his culture. However, when he is with his friends or at work, he adapts to the larger American culture. As such, he has been able to hang onto his own culture, while still adapting to a larger system of values (American).
Yes, it surely CAN work. But I prefer a homogeneous society, and I suspect many other Swedes do.
It may work where you live, but I really think people want to "feel at home" and with people they connect with on a cultural and behavioral level.
There is a known study on trust within communities, diversified compared to monoethnic. People don't like it (like you could have guessed easily). People tend to stay with their own, especially when they are not really welcomed and effectively integrated (and they need to want this too).
It's pretty obvious even in your own description, you see him as Indian, not as a American, but you both are supposed to be.
But the larger issue is with Islam and its people and its origins in a far-away middle age type culture. When the cultures are so far apart, like Swedish secularism and hardcore Muslims, the clashes really start. Food, special rights, treatment of animals. Alcohol. Language. Views on women, violence.
These people seem VERY opposed to becoming Swedes at all, they want to (-or like I fear, unwillingly and AUTOMATICALLY do-) move the middle east into their own neighborhoods right here in our country, and it sucks that they are allowed to.
It's not like they do their little prayers and go to a mosque now and then, and then adapts like your Indian friend, their very different view on society affects us. And that's not even talking about how they affect us economically, I'm just on the cultural aspect here.