I don't think there is any useful conversation to be had re: "forgetting" that public data. It's a matter of fact. Once data is public it's public. There no magical "forgettable" bits for special classes of digital data.

Deleting copies pof data from public and quasi-public forums isn't practically possible, short of taking away everybody's general purpose computer. I don't think that's going to happen (and I certainly wouldn't want it to).

I think it's just a world we have to live with. I don't particularly like it, but I don't have a choice in the matter.