No, they're not. Just like Altamont Press is not responsible for the c**p that stifles the actual rail-related content here so often. The posters are responsible for their own content, and if something is bad enough to trigger a lawsuit a lawyer might ask for IP addresses or other information from AP to help identify that person, and AP might be forced to remove that person's content. Same thing with copyright: if copyright is violated and a complaint made, AP is required to remove the content; there's an automated process for dealing with that in places with more activity (like Youtube, FB, etc.).