They all do it from the very beginning. So you're either left with social media without any algorithm to steer content you might like to you - in which case, why bother - or what we have now.It isn't unfair in principal, however once you do so you are no longer a platform, you are an editor. The social media giants want to have their cake and eat it too by enjoying the benefits of both.
But the publisher/platform thing isn't a legal distinction that matters. Section 230 is clear on this, and it was true even before Section 230. Further, there has never been a requirement that platforms be ideologically neutral.