The data was harvested by the Facebook pixel as part of their audience building tech for acquisition of new customers. So you are being sold by Facebook, Backblaze just happens to have been quite careless here but they are not "selling your data".

The breach of trust is BB letting third party code on their platform and especially from a particularly untrustworthy third party. That's it, it's egregious and should be taken seriously, that also means discussing it seriously.

This kind of hyperbole is counter-productive, it only makes it easier to ignore your concerns as "crazy overreacting".