Not really a surprise to anyone. And also probably inevitable for most of the same reasons that media bias exists. Facebook was hiring young journalists to select "curate" what its news feed showed. Their politics probably dictated the rest.
Facebook workers routinely suppressed news stories of interest to conservative readers from the social network’s influential “trending” news section, according to a former journalist who worked on the project. This individual says that workers prevented stories about the right-wing CPAC gathering, Mitt Romney, Rand Paul, and other conservative topics from appearing in the highly-influential section, even though they were organically trending among the site’s users...
“Depending on who was on shift, things would be blacklisted or trending,” said the former curator. This individual asked to remain anonymous, citing fear of retribution from the company. The former curator is politically conservative, one of a very small handful of curators with such views on the trending team. “I’d come on shift and I’d discover that CPAC or Mitt Romney or Glenn Beck or popular conservative topics wouldn’t be trending because either the curator didn’t recognize the news topic or it was like they had a bias against Ted Cruz.”
The former curator was so troubled by the omissions that they kept a running log of them at the time; this individual provided the notes to Gizmodo. Among the deep-sixed or suppressed topics on the list: former IRS official Lois Lerner, who was accused by Republicans of inappropriately scrutinizing conservative groups; Wisconsin Gov. Scott Walker; popular conservative news aggregator the Drudge Report; Chris Kyle, the former Navy SEAL who was murdered in 2013; and former Fox News contributor Steven Crowder. “I believe it had a chilling effect on conservative news,” the former curator said.
No doubt. Especially since Facebook is now the other nerve center of the internet, besides Google. Google dominates search. Facebook dominates social media. Between them they determine where the traffic goes.
While this form of bias was supposedly decentralized, pushing Black Lives Matter was very much dictated from above.
“Facebook got a lot of pressure about not having a trending topic for Black Lives Matter,” the individual said. “They realized it was a problem, and they boosted it in the ordering. They gave it preference over other topics. When we injected it, everyone started saying, ‘Yeah, now I’m seeing it as number one’.”
So Facebook rigged the game. Mark Zuckerberg has made it pretty clear that he wants input and policy level involvement in all sorts of issues. And for now we're talking news feed, but you would have to be very naive to believe that algorithms in Google and Facebook don't have their own political biases built in.