Hacker News Reader

They actually buy a ton of data from others. So they are encouraging a market that thrives by selling our data without our informed consent.

Very true, and very bad, but not the same thing as selling the data themselves.

I hadn't heard of this recently. Where could I read more about it?

Not GP. I don’t want to link to one or two specific sources, but you can find many reports by searching for “Facebook buying offline data”.