Facebook and others are not responsible for what their users upload and enjoy the legal protection that comes from it. If they decide that they are going to be

Facebook and others are not responsible for what their users upload and enjoy the legal protection that comes from it. If they decide that they are going to be curators of content on their platforms, they are no longer a mere service provider, but a publisher. They might find those protections vanish, which would more or less destroy their platform.