As a person who works in IT, and from my own personal point of view, I agree that I find it hard to imagine that someone would sign up to FB without clear awareness that feed manipulation and other shenanigans might occur[0]. But the thing is, people are doing so every day.

Most people on FB are using FB assuming it's a utility something like email, without realising that it is like email, if email had its own agenda. It's really easy to forget that most people in this world do not live/work in the echo chamber that we do. When I talk to them about the issues, sure, at best they might profess to understand or even be concerned at the time of that conversation, but by and large they won't change their behaviour and the conversation will be quickly forgotten.

Never underestimate the indifference with which people can view the inner workings of technology.

0. I see the fact that I find this hard to imagine as a form of "Expert Blindness" or "Knowledge Blindness". If someone has a better or more accepted term for this phenomenon, I'd like to hear it.