I think it is inherently a good concept, that people should transcend their cultural differences and live harmoniously together while respecting differences.

But it cannot be practiced without a solid foundation in moral law, which is why multiculturalism is failing in the secular west.

The problem with multiculturalism without moral foundations is that you have no basis to say what is right and what is wrong. So things that are inherently wrong will be defended on the grounds of cultural differences, and things that are inherently right will be dismissed as products of cultural hegemony.

That's why you have some people saying "being on time is white supremacy" and then at the same time not prosecuting child rapists because "it's allowed in their culture"