For example, T-Mobile is a platform. They aren't responsible for anything you say when on the phone, using their network.
CNN is a publisher. They are responsible for anything that gets posted on their website, and can get sued accordingly.
Social media companies want to choose what is posted on their website, but also not be held responsible for anything that is posted on their website. They want the perks of being a publisher, and the perks of being a platform.
Obviously there are arguments made on both sides. But that is the general disagreement, if I understand correctly.
This isn't true though. CNN/NYTimes/etc can't be sued for 3rd party comments on their site. CNN is also allowed to filter what comments make it on their site. These are not opposing ideas.
I grew up reading the NYTimes online and thought that the discussion section offered great debate. I think it might have become a case of it is too expensive to moderate? Do people just post ads and spam? Because in my mind, active discussion is always good