Because Facebook's algorithm decides what appears on each users' news feed, by that, even though it's an algorithm without human intervention, it can be said that filters / censors content.

If it wouldn't filter out content and it would just show every bit of content that each user uploads on each of their friends' news feed, it wouldn't be a problem. In Germany if you act as an editor over content (whether it's a script or human) it comes with responsibilities.