That's clearly what you are in Facebook's opinion - experimental subjects, just like rats in a laboratory. (Bold underlined text is my emphasis.)
Over 600,000 Facebook users have taken part in a psychological experiment organised by the social media company, without their knowledge.
Facebook altered the tone of the users' news feed to highlight either positive or negative posts from their friends, which were seen on their news feed.
They then monitored the users' response, to see whether their friends' attitude had an impact on their own.
. . .
Facebook were able to carry out the experiment because all users have to tick a box agreeing to their terms and conditions. These include "internal operations, including troubleshooting, data analysis, testing, research and service improvement."
In the study, the authors point out that they stayed within the remit of the agreement by using a machine to pick out positive and negative posts, meaning no user data containing personal information was actually viewed by human researchers.
There's more at the link.
I'm sure you're happy to know that agreeing to such an innocuous-sounding clause in Facebook's service contract might expose you to being the uninformed subject of psychological experiments. Is that creepy, or what? It's yet another reason why, IMHO, no-one in their right minds should be on Facebook at all. They treat you like a laboratory rat in so many ways that it's become almost dehumanizing.