The press you mention is legally accountable for its content. Platforms have protections. Telephone companies, for example, aren't responsible if you slander someone over the phone and they send the audio to the recipient.
Why shouldn't platforms be stripped of their legal protections (and some effectively destroyed) if they are exercising editorial discretion? Why shouldn't YouTube be responsible for the videos that they do allow/have approved?
If someone doesn't think that YouTube should be accountable for content, then should a newspaper be accountable? Should a person be accountable for his content?