I don't see what else you want. In 2014 it was revealed that Facebook did run experiments to see how much of an impact they can have on people's sentiments. Just check the study, it's public:
https://www.pnas.org/content/111/24/8788.full.
The researchers found out that Facebook's news does influence sentiments in a contagious manner. Which implies it does result in behaviors change on the platform, otherwise they don't have a way to measure the effect in the first place...
And don't forget to check the Acknowledgement section:
> We thank the Facebook News Feed team, especially Daniel Schafer, for encouragement and support; the Facebook Core Data Science team, especially Cameron Marlow, Moira Burke, and Eytan Bakshy; plus Michael Macy and Mathew Aldridge for their feedback.
It's not like they hide it, that's exactly why advertisers and political parties partner with Facebook in the first place.