There's a great story in The New Yorker (the abstract is here for non-subscribers) about the social situation in Amsterdam. Apart from being an interesting snapshot of the city, it's also a fascinating look at the problem of tolerance. Amsterdam has always prided itself on being the city of tolerance - and on my visits there I've loved the fact that (much like Cape Town, though there it's less by accident and more by design) you can walk across the Dam or down Kalverstraat and rub shoulders with Muslims, gays, liberals, conservatives, whites, blacks, locals, foreigners, Jews, and pretty much everybody who doesn't fit into the vanilla flavour of some of Europe's other, less complex, cities.
But, much as Amsterdammers try to promote their values of tolerance and acceptance, they're finding that some of the people they're... erm... tolerating aren't quite as... y'know... tolerant as they are. And that's the whole problem, isn't it? You let anybody into your society, and you'll soon find that some of the people you let in have no desire to fit in, and wouldn't ever let you into their societies. It's a social and philosophical problem that will, I sense, shape this century.
Of course, the simple answer is to just let them all eat stroopwafels.