The difference is that the internet has discontinuously more scalable network effects, so technology companies often find themselves in a winner-takes-all dynamic. If some publisher, newspaper, or literary magazine refused to publish Walt Whitman, he could always try and find another publisher. But if Twitter bans Titania McGrath, there is no other Twitter for her to join because the next best alternative has 1/10000th the number of users.
This effect is new. These platforms are private entities, but effectively they operate as public commons. So culturally we must treat them similar to public commons where it isn't acceptable to kick out quirky characters because some of us don't like what they have to say.