Facebook is also part of a network of other American Social Media companies that have automated systems to block content posted that match certain patterns and known propaganda efforts by other nations.
Recently an anti-TPP website was blocked simultaneously across several communication providers (https://www.reddit.com/r/technology/comments/38pmg8/hey_redd...). This was a mistake as the website name closely matched the name of a Russian Anti-TPP propaganda campaign.
The mere existence of the ability to coordinate content blocking across service providers means that a censorship network exists - the question becomes whether it is 'abused'.
It's difficult to ascertain abuse, of course, given the Obama Administrations policy with regard to censorship and propaganda and its weakening of the Smith-Mundt Anti-Propaganda Act. The Administration believes that the US government is not responsible for having its influence operations online spill over to affect American people - it is merely prohibited from actively and specifically targeting Americans. That is, the new policy is that it's okay - even expected - for Americans to be 'collateral damage' in censorship and propaganda campaigns.
Thinkers like Cass Sunstein are traded high up in the US Government - Sunstein wrote a book on the 'Problem of Free Speech'. Broadly this influential Washington Legal Scholar believes that speech that is actively harmful or misinformed can and should be 'addressed' by the state - and he recommends ways in which that can happen.
The Snowden documents reveal that (so far as we know non-specific American targeting) the mass surveillance networks are intrinsically tied to influence operation capabilities - outside those capabilities at the GCHQ (which legally are not prevented from targeting Americans) - and who engage quite heavily in psychological influence campaigns.
I have personally, repeatedly witnessed Facebook selectively block posts of mine linking Wikileaks material, the Snowden documents (when they were first being published), and leaked drafts of the Trans Pacific Partnership and watched as others complained about having their posts trying to organize protests on May Day blocked similarly.
It's true also that Facebook has been associated with at least two studies on societal manipulation programs with researchers that are funded by the Department of Defense in the same area. Many people remember the "Emotion Manipulation Study" - fewer the vote influence study. These sorts of programs have been called for in the past 10 years of Defense Document planning and DARPA today, under their SMISC program, study similarly how to shape and track ideas in social media networks like Twitter.
I'm honestly glad that the EFF is finally giving this issue some attention.