Ethnicity is a social construct.
... yes....?
...I would love to read, whether that had anything to do with defining blackness or if it was a comment on my post.
It means that there's little point in trying to "define" it.
Depends how interested you are in Atlas as a "subculture". Social constructs are a constant negotiation and it is potentially interesting how we as a group define a concept like blackness compared to how other groups and society at large do it, since the forum is so unrepresentative.