There are two parts to it and this is something that I was discussing with someone just yesterday.
1. How easy is to fit in?
2. How much does one want to fit in?
1. How easy is to fit in? Stark Differences b/w US and Europe
The US really is the ultimate melting pot. If you became part of a student body or the workforce and started living in some neighborhood, people won't bother you and you won't face many problems fitting in. And frankly, anyone who's serious about getting a green card or something will do everything to fit in and will avoid trouble at all costs. You won't find many neighborhoods that are 100% Muslim because Americans don't sideline someone just because of their religion. So, their isn't a need for Muslims to congregate in the same parts of the city. Its easy for an immigrant to fit in. I mean let us be honest, if the US hadn't opened its doors, none of my countrymen or my Paki brothers would have ever tasted success. There would never have been any immigrant CEOs. But the US doesn't work like that. You can get to the top.
On the other hand, if you look at Europe, even places like Denmark which were basically open to letting everyone in a few years ago, Muslims are not exactly welcome now. Belgium has its own problem. One has to ask, why are there Muslim neighborhoods in Belgium and not in the US, and that is what someone did ask:
Why there are Muslim ghettos in Belgium, but not in the US - The Boston Globe
My point is that Europe has had a problem with letting people in and then discriminating against them to the point that the immigrants actually believe its important to stick together for the sake of survival.
It was funny to me that Indians and Pakistanis who're always talking about nuking each other, hang out so wonderfully in Britain, as if they hadn't spent the last many decades fighting wars. That's almost like finding neighborhoods where Israelis and Palestinians live together. The reason why they had to stick together was because they faced a kind of segregation in Britain that Hitler would have loved. And it wasn't just Muslims, but anyone from that region found a hard time fitting in unless they went to this neighborhood.
Europe has a problem. It doesn't let people fit it even if they want to. So, when some second generation muslim youth asks the "wrong" people why he doesn't have the right job, the right lifestyle, the right stuff, the answers he gets related to Europe suddenly all make sense - even though they are lies.
2. How much does one want to fit in?
You know if I want to make something of myself in a foreign country, I will have to fit in. But, there have been many cases in Europe where people have come into the office wearing traditional clothes and 1 time out of 100 someone reports them to HR and then it blows up to be a big story. But, to me its like, if I am working for someone, I better dress for work. Do in Rome as romans do. Of course, France went way out of context when they banned all headwear and stuff from schools and workplaces. Now that is used by terrorists to misguide the youth, "Hey, look. They don't want you here."
French ban on Muslim headscarves is upheld by human rights court | Daily Mail Online
Multiculturism hasn't failed in the US. In fact, it would have worked in Western Europe too had Europeans actually tried. And it hasn't failed in all Western European countries too - Germany has tried to get things to work, although now the situation is not that great. It's not merely about Islam in Europe, it's more about race and language. Europe created the "Us vs Them" at the level of the government, which is a terrible thing.
So, there is something that is wrong on both sides. And it needs to be fixed fast.