Plus it's their network, they likely have TOS allowing them to do anything on it. Probaly except altering the posts (... but they replace links with their shortener i think).
* If someone criticized newspapers for yellow journalism and inciting violence with sensationalism, would it seem so weird to push the newspapers to "essentially become fact-checkers for the content posted" on them?
* Is the way that people view large public figures on social media all that different than how they did with newspapers?
I think it is important that there is a diversity of avenues toward publishing, so that incorrectly judged messages / messages that the population disagrees about the harm of can still be published somewhere, but it's never been easier than now to publish things to the web even without the help of a specific individual platform like Facebook. The web isn't just Facebook.