There definitely isn't a thing such as "caucasian culture" because the indigenous populations of Europe are far too varied to have that low level of commonality.

Sure. "Caucasian" is a broad general category, tho less general than "white." As someone who hasn't read much cultural anthropology, It seems to me that cultures are determined by geography, and the tribes, nations, the various collective arrangements humans have formed to survive in different physical environments confer "identity."

So why do so many insist that there is such a thing as "black culture" and at the same time claim there is no "white culture"? To denigrate people with white skin regardless of whichever culture they are raised within? I mean, it's obvious that there are real differences between a Lithuanian, a Russian, and an Englishman, as well as differences between a Zulu, a Bantu, a Chicago ghetto black man, and so forth.

Divide and conquer.