Their tagline is "Fair and Balanced". In reality they're nothing of the sort.
Here is a link describing how Trending topics works:
https://www.facebook.com/help/737806312958641
Where does it state Trending topics is a neutral source for unbiased news? They admit readily that an algorithm does much of the work, but that it also relies on human intervention. And the Valley, including Zuckerberg, have worn their "liberal" ideals all over their sleeves via their actions.
They sold people on a tagline, while never really being up front. Need I again quote Zuckerberg's infamous opinion on people trusting him? Let's not forget his shenanigans in India with "free" but hobbled internet.
They're as open about how things really work as Fox. Unless Fox is suddenly inviting people into their meetings where editorial directives are discussed. They put some friendly language on there, making a vague claim, then feed people bullshit.
The mental gymnastics people go through by blindly accepting such shallow rhetoric like "Fair and Balanced" or "We're neutral" without really verifying is bizarre.
Facebook has competition in the form of dozens of news aggregators; Apple, Google, Microsoft, Pocket... This is about one feature of Facebook. Not the entire enchilada.
My frustration is not with Facebook lacking competition. It's the aforementioned obtuse behavior of the populace at large, the mind-boggling mental gymnastics being employed, in thinking that these large, opaque corporate machines are focusing on the end user. The phrase "if it's a free service, you're the product, not the customer" comes to mind. Facebook sells eyeballs to others. They have little interest in being neutral.