[HerraBRE]

This is a legitimate concern.

I would not put it past Facebook (or other businesses which are addicted to harvesting user data) to behave badly against networks like this. However, for the sake of their reputations they'd still probably do it quietly, which means many of the person-to-person attacks that deletion protects against would still be thwarted.

This is a problem the same way Facebook's privacy controls are a problem. Facebook themselves are not bound by them, but they're still useful if you want to protect your data from other users of the platform.

And FWIW, I think most of the big crawlers respect robots.txt - this is the same sort of thing.