What killed Western culture?

Conservatives rightly blame postmodernism and its creation of subcultures and a relativity of values for the fall of Western culture, but that alone does not explain the fall.

Homogeneity defined merely as the middle and upper classes reading the same books and listening to the same music was not the only homogeneity fractured, it was also the ethnic homogeneity of Northern Europeans reading the same books and listening to the same music which was usurped by other naturally competing ethnic groups and cultures.

So why can't even paleo and traditional conservatives admit this since we won't recover from a problem if we can't mention its main causes?

It seems to be a combination of fear of being called a racist, and from the non-material, spiritual, universalism inherent in Christianity, or from both. Careers can be destroyed if one is labeled a racist, and crossing basic tenets of ones religion is too traumatic for most folks. Also the successful leftist propaganda of labeling race-affirming as "race hate" was helped along by real race haters usually not of the tradition-sustaining middle and upper classes. The Alt-right seems to have grown from its willingness to mention "race."

The biological origin of much of our social behavior needs to be admitted if we wish to save or revive Western culture. And God need not be lost when real supermaterial Godhood is understood as evolved to in the material world where successful survival and reproduction have always come from group and ethnic selection. 

We need to find a way for this real human nature to allow all groups to prosper, which I believe will come from an ethnopluralism of ethnostates. protected by federalism.