Facebook became the world’s most dominant conduit of news and information but said it would remain neutral to what spread through its channels. Meanwhile, a handful of engineers were building algorithms to decide which of its 2.2 billion users would see what.
By remaining agnostic about which influencers rose to popularity, and helping them along by building recommendation and newsfeed algorithms to enhance that popularity, Facebook allowed Russia to rapidly gain influence on the site, says Nicholas Christakis, a physician and sociologist at Yale who studies social networks.

Source: Why Was Facebook So Easy to Hijack? – WSJ
The entire story in the Wall Street Journal implies Russia is the predominate propagandist on Facebook, dominating and controlling public opinion.
Look at your friend’s Facebook posts. Those that share posts predominately regarding political issues are themselves propaganda activists seeking to use FB to persuade others to adopt their own agenda. The overwhelming quantity of propaganda comes from your own friends. (See update, below).
Individuals, informal “club-like” groups, formal organizations, industry, the media, academics and government all use Facebook for active propaganda operations. To suggest that Russia is the predominate propagandist on Facebook is reckless, foolhardy and empirically false.
Social media is a swamp of propagandists and propaganda messaging having nothing to do with Russia, China, Poland, Israel, North Korea, Britain, Japan or any other country.
Social media is a frictionless platform for the spread of propaganda. No government broadcast license or printing press required. Anyone can be a propagandist today. Propaganda operations are not limited to Russia-based Internet trolls!
The inherent model of social media is a platform for propaganda operations. That is the fundamental root cause issue.
UPDATE: Hah hah. I just looked on Facebook and see “friend’s” sharing or posting their own propaganda saying, basically, that foreign state actor propaganda dominates social media and threw the U.S. election. The irony is that none recognize their own role in propaganda messaging as both willing targets of propaganda, and as active participants in using social media to spread their own propaganda messaging.
They are unable to see that nearly everything on FB and Twitter is propaganda messaging – and that propaganda overwhelmingly comes from your own friends, not state actors.