Of particular concern are "shadow profiles" - dossiers on people who have never even used or consented to using Facebook[1]. I'm no lawyer, but there could be precedent per this Vizio case.
In my opinion Facebook is hugely overstepping people's privacy bounds, even if they do bury what they do with some of the data in their terms of service. I never even knew about DeepFace, or mouse cursor movements, or any of the multitudes of violations of privacy outlined in the article below, and frankly it scares me and makes me angry.