I worked at Facebook on ranking systems at that time. No, facebook was not trying to intentionally provoke any emotional response. They were trying to increase product metrics like number of videos watched, subject to constraints on the % of watches that include things like violence or bullying. Ultimately the goal is to make the Facebook product good so they can continue selling ads.

Facebook would make all its users happy and positive if that were possible to do. Nobody at Facebook is trying to manipulate you, except by trying to show you content that keeps you coming back to Facebook.