Exactly. I understand that if I give away my social profile and/or pictures to a large corporation that they may be abused by said corporation. That's what corporations do.

I choose not to do so, I don't use facebook or gmail, but if I did I would only expect them to be using and abusing it, not some secret government program.

But why would such an expectation be reasonable? Surely once you have given the information away, it's their business what they do with it?

Precisely: many if not most websites have Google Analytics JS, so you're being tracked around the web (ghost profile) even without a google account.