I think most libs would just say that racism and xenophobia are inherent to tribalism, which is inherent to the human mind as an evolutionary trait.

This is still Idealism. The concept of “Human Nature” is nebulous, and changes throughout history. Materialists assert that what is considered “Human Nature” is reinforced and created by Mode of Production, Liberals just claim Capitalism to be natural and the default state of humanity. The difference is that Materialists have historical evidence, whereas Liberalism stands against historical evidence.