Maybe it's a lot of young people fresh from college and they hear about the big five or whatever, and choose Facebook because they think of it as a social networking company and big, famous, and cool. Just an old guy's opinion - would not want to work there.
That explains the actions of (some of) Facebook's "rockstar" developers. That does not explain the actions of Facebook's data scientists, psychologists, product managers, and execs.
Occam's razor - They knew, and perhaps they cared, but they cared far more about their salary and climbing the industry ladder to say no or blow the whistle.
You cannot really expect people who have to work for a living and do work for a vertically structured corporation to be ethical and to go against their bosses. The problem is inherent to capitalism and it can make people do far worse things than this, like killing people or promoting and making wars.
Yes you can. Doing the right thing at the expense of a comfortable lifestyle is a problem every generation has faced. Washing one's hands of responsibility in such a way is a rather lazy argument.
The conscious and deliberate decision to put a system in place that manipulates and exploits people who have to work for a living and makes them do things with no questions asked is not created by employees themselves. But it is a decision nevertheless and it is unfair to expect employees, who are victims of such system, to do the right thing as they usually fear the consequences of the dissent. Which can literally mean not just losing a job, but life and death kind of choices, never being able to afford a medical care, lack of place to live, prison and so on.
For execs sure it's about managing the product, i.e. the users, especially in what we've seen in public statements from Zuckerberg and Sanders.
For the data scientists and psychologists, it's a chance to work on large scale data/populations and test all sort of theories and hypotheses on a large scale, probably unavailable anywhere else except Google and Amazon as postulated here.
I imagine it's a dream job in that respect, where one gets so caught up in the work the consequences don't matter to the worker until the 2016 US election (Trump got about 25% of the vote in the Bay Area) or Brexit referendum and now these investigative reports.
