Yes. Ad revenue is definitely their cash cow, but the social experimentation has been another major source of income, both in terms of data they can sell and data they could use to improve the impacts of their platform. They've been surprisingly open about some of the experiments, as they've had impacts on how their algorithms work, but even then, there's been little in the way of regulations let alone ethics.

And it isn't just Facebook - reddit has performed social experiments on its user base as well as other companies, except that, as for the experiments revealed to the public, Facebook has admitted to adversely impacting the livelihoods of large groups of users.

In one experiment that Andrew Marantz cited in his book, Anti-social: Online Extremists, Techno-Utopians, and the Hijacking of the American Conversation, Facebook intentionally subjected one user group to positive posts and news articles only and another to negative content. Those exposed to the negative content expressed emotional distress and evidence that their quality of life suffered at a worse rate than at the rate that the other group, exposed to positive content, saw their livelihoods improve. And it's thought that this is one of the more impactful experiments when it came to tuning the overall algorithm behind Facebooks news feed.