again, I do not think Facebook is a publisher, but rather a platform, so I do not see how the parallel applies.
At any rate, if you are asking why censorship, I guess there are angles and perspectives from which it is not, but that risks becoming a path to various dystopian scenarios (freedom of expression/speech negatively correlates with authoritarianism of governments, for example)
If you want to publish something and some publisher does not want to publish it for you, chances are you can find a different publisher that is willing to, without necessarily negatively impacting the spread of your content and ideas.
For platforms such as Facebook that is fundamentally different: A- they gain their power by offering a service, not spreading ideology... users come to them to access content produced by others, so their influence to the content that they are, or are not, able to access is "unfair" and should be in my opinion unlawful; B- exclusion from them pretty much disconnects you from a large amount of fellows humans in a significant way.