What is the goal of multiculturalism? To maximize the number of existing cultures? Why would anybody want that? If you want to keep a maximum number the only solution is to prevent interaction between different cultures, ergo one form of apartheid or another.
Multiculturalists comes mainly in two shapes, ethnopluralist (often inspired by McCulloch) and the mainstream PC liberal one. The first is more honest, not denying that any serious approach to "ethnic rights", and so on, means global apartheid. The liberals, as always, are hypocrites.
What happens if you put people from 57 different cultures in one place? The answer is culturecide, if returning one hundred years later you will find not 57 different cultures but a significantly lower number, perhaps just one.
There is a lot more that can be said about this. Take only the repulsive westernization that strikes every part of the world, this is the largest ethnocide ever conducted - but the liberal hypocrites who a minute ago praised diversity remain silent. Not to mention the very notion of any kind of "universal rights". We see here that the liberal pluralism is as shallows as always. Everyone is permitted to have their "native" food and clothes, as long as they subject themselves to the ways of the petit bourgeois.
The problem of westernization is not that it's ethnocidal per se. There is no reason to shed any tears when people stop believing that we live on a great turtle, stop wearing "ancient" national costumes or give up rites at solstice. All such phenomenon has little to do with the true Tradition which lies deep under the surface. In the words of Julius Evola:
There is a superior unity of all those who despite all, fight in different parts of the world the same battle, lead the same revolt, and are the bearers of the same intangible Tradition. These forces appear to be scattered and isolated in the world, and yet are inexorably connected by a common essence that is meant to preserve the absolute ideal of the Imperium and to work for its return.
The problem of westernization, and the inevitable culturecide that follows, many times lies not in the customs destroyed but in the values brought; convenience, materialism, "reason", cowardice and others. To sum up, emasculization.
All this does not mean that we should be (real) multiculturalists, on the contrary. It is an all to common mistake to simply watch the enemy and then act in whatever way is the direct opposite. We are every bit as culturecidal, the difference lies in what we strive for; the rise of our geheime Deutschland and the creating of a Weltstaat based on the ancient Prussian befehlsprinzip - To serve obedient and to command with humility.