Safe harbor is effectively dead. Recent changes in law make neutral content hosters liable for the content their users create/upload/share (going beyond the standard strictly illegal stuff like child porn, inciting violence, etc).
(I work for Google, but I don't have any inside information on this; it's just speculation.)
Section 230 of the Commucations Deceny Act of 1996 "allows ISPs and other service providers to restrict customers' actions without fear of being found legally liable for the actions that are allowed."
"The act was passed in part in reaction to a 1995 decision which suggested that service providers who assumed an editorial role with regard to customer content thus became publishers, and legally responsible for libel and other torts committed by customers. This act was passed to specifically enhance service providers' ability to delete or otherwise monitor content without themselves becoming publishers"
Source: https://en.wikipedia.org/wiki/Section_230_of_the_Communicati...
https://www.npr.org/sections/alltechconsidered/2018/03/21/59...
https://www.npr.org/sections/thetwo-way/2018/03/23/596460672...
To use an analogy: Sec 230 is like a "Good Samaritan" law that protects people who try to help accident victims from liability for their actions. This is obviously good public policy, because many people are scared of being sued if they make any mistakes (or even if they don't), even though the evidence points overwhelmingly to a net positive effect of such attempts of help.
Backpage used Section 230 like a guy punching someone in the face and then claiming they were trying to protect them from the mosquito sitting on their nose.
The new law assigns liability if you are grossly negligent in allowing certain content to flourish on your platform.
But, the important point is: this liability is independent of any moderation platforms may or may not engage in. The attempt to moderate some content still does not increase your liability.