Book distributors generally will carry any book given them by a publisher, regardless of content. Twitter is engaging in moderation, which puts them not just i

Book distributors generally will carry any book given them by a publisher, regardless of content. Twitter is engaging in moderation, which puts them not just in the business of distribution. They are playing the publisher role - receiving content from authors and deciding whether or not to publish it. That is the very definition of a publisher. And yes, publishers can indeed be sued.