@Ishmael: "What does this have to do with 白左?"
OP in this thread illustrated how 白左 could be used (for example) to describe people who appropriate pieces of other culture, in that case the Chinese qipao.
Whether that example was correct or not in reference to 白左, is rather irrelevant to the comments that followed.
When we are talking of language (any language), we cannot forget that purpose of language is to describe real world.
That purpose would be doomed to fail, unless we can to some degree agree about what that real world is.
In this case, what is cultural appropriation to begin with.