Multiculturalism is ...

... the elite management of group social conflict (and the solicitation of such conflict to be managed by such elites) through the conversion of sensibility, chiefly resentment, founded upon group identities of ethnicity, race, gender, and religion into universal and legally and bureaucratically enforceable claims of human rights; with the consequence of displacing the hithertofor liberal content of those rights while yet still proclaiming a universal liberal basis for these new multiculturalist, sensibility-resentment-based claims of rights.

(Multiculturalism is not really capturable in a one sentence definition, of course, but I thought I'd give it a try. No doubt I will amend it down the road.)