I don't find statements like that particularly helpful.

It is fair to say that most organised attempts to advocate for 'White Culture' -such as White Pride events and a staggering proportion of 'European Students Associations' etc are explicitly racist in practice. This by itself should be concerning enough to lead observers to scrutinise very carefully organisations or publications devoted to securing 'White Culture'.

This is a factual statement. But I see how it can be seen as an emotionally charged one.

White people are too ambigously defined a group to have one common culture. Hence the term is nonsense.

Black culture does not exist.

Is this statement morally equivalent? Why or why not?

I don't think this is a moral question, but rather a question of reality. Black culture does not exist globally. Black culture of the United States does exist, because black people in the U.S. have a common history and common societal experience that binds them together.

White people are too diverse a group to have one single culture. I am white and not from the U.S. Based on these facts people cannot guess what my values are, what my traditions are, whether people of my ethnicity were ever opressed or were the opressors, or even what language I speak, or what religion I have. Hence the term "white culture" does not make sense.