My understanding is that it protects the web site owners from lawsuits about content from users. That has always seemed like a tricky line and maybe a false line. The line between the site and the users. The owner is the site owner. In my view as soon as a user posts text or images on a site they do not own that. But this is because I reject the idea of IP altogether. The site owner is the true owner of the server or they are renting the servers.

Been a while since I read the cases against libel and slander laws. I don't recall the arguments against them. I assume you mean completely free speech vs. what is in place now in the US.