Multiculturalism is part of the Postmodern/neo-Marxist ideology that declares that all cultures are equally valid and to be venerated and protected, except for Western Culture, which is declared to be evil. It is thus essentially the application of Marxist Critical Theory to Western Culture. The assertion that all other cultures are equal results in moral relativism; what is considered moral in one culture might be immoral in another, excluding Western Culture.
Note that the elevation of cultures above the Judeo-Christianity of the West serves to undermine the preeminence of Judeo-Christianity in the West, whereas prior to the introduction of political correctness, the concept was that people of other cultures who came to the West were to assimilate into the original Judeo-Christian culture.
Critique: The position that all cultures are equal is only tenable by massive language deconstruction and ignorance of facts (see Postmodernism). Each culture has their own strengths and weaknesses, and these often change over time. And there are some cultures – such as Islam’s Shariah – which are simply incompatible with Western culture.