Are Some Cultures Better than Others?
The trajectory of progressivism ultimately leads to the denial of self by promoting the other. This self-destructive way of thinking runs counter to our ingrained survival instinct. And by extension Europe, by all statistical analysis, has already lost its instinct to propagate the species.
Multiculturalism as an experiment fails because it is based on cultural relativism, meaning that it's an egalitarian political doctrine that presupposes all cultures to be equal in every way.
Here's the rub, the indigenous society's morals and values must then cease to exist as a consequence of equality. Therefore social norms cannot be applied to the invading--but equal--culture. How can one culture apply its morals and values on an equally viable culture, the argument goes. Europeans have not figured this out yet. They have precluded themselves from their own culture in the process. Bad move, Europe!