There's a phenomenon in left-wing circles where initially reasonable statements and concepts get repeated ad nauseum until they not only lose their meaning but transform into deeply bigoted ideas.
The idea "there is no single white culture," is true because white is a concept created to describe the powerful position in Western societies. There are many different cultures, who's members are often white. But this idea became "white people have no culture" which is just not true, deeply dehumanizing, and harmful, especially to people who look white but experience marginalization because of their culture.
Another example might be cultural appropriation, which perhaps should be understood as a misrepresentation or exploitation of the cultural practices of another, especially where the person exploiting does so for personal gain, without acknowledgment. But now, people have basically transformed this into "when somebody does something from a culture they weren't raised in" or "when a particular race or ethnicity behaves in a way that's different from how they normally do" which promotes racial and cultural stereotypes and attempts to control the behaviors of people based on their race, ethnicity, and culture.