"Real diamond" as opposed to zirconia, or did you mean natural diamond (as opposed to a real artificial diamond)?
Edit: As I said in another reply, there's nothing illogical about it. If value is placed culturally and socially on natural diamonds, then they are valuable, regardless of if that value is "artificially" created via advertising of whatever. Lots of stuff is quite stupid if you look at it objectively, out of context. Doesn't mean it isn't true in context.
EDIT: Just did a ctrl-f for NFT and I guess I wasn't the first to say that, although those comments are much lower on the page.