The irony of multiculturalism as a political process is that it undermines much of what is valuable about diversity as lived experience. When we talk about diversity, what we mean is that the world is a messy place, full of clashes and conflicts. That's all for the good, for such clashes and conflicts are the stuff of political and cultural engagement.
(...)Multiculturalism, on the other hand, by reposing political problems in terms of culture or faith, transforms political conflicts into a form that makes them neither useful nor resolvable. Rather than ask, for instance, "What are the social roots of racism and what structural changes are required to combat it?" it demands recognition for one's particular identity, public affirmation of one's cultural difference and respect and tolerance for one's cultural and faith beliefs.
Multicultural policies have come to be seen as a means of empowering minority communities and giving them a voice. In reality such policies have empowered not individuals but "community leaders" who owe their position and influence largely to their relationship with the state. Multicultural policies tend to treat minority communities as homogenous wholes, ignoring class, religious, gender and other differences, and leaving many within those communities feeling misrepresented and, indeed, disenfranchised.
Britain's brand of multiculturalism has failed because it placed at its center the cult of diversity and thus sacralized differences in the name of culture and of religion making moral judgments difficult and segregation/sectarianism unavoidable. I'm uncomfortable with drawing sharp distinctions between Britain's multiculturalism and diversity because in the mind of too many those two concepts have merged. Nowadays, people who argues fanatically for diversity are in fact doing so by categorizing people, by hierarchizing particularities, and thus deciding which ones ought to more important than others. The trouble with both multiculturalism and diversity as they are commonly understood is that they lead to desindividualization. People are forced to identity with a group of people in order to matter and to avoid marginalization because identity politics is the most potent form of politics.
To put things more simply, the only acceptable multicultural society is one, which sees that people as individuals, not as member of a group/community/whatever else and recognizes that culture and particularities are never legitimate justifications for the erosion of the social compact and the unjustifiable.