I'm personally of the belief that network effects have granted Twitter a relatively unassailable cultural position, or at least enough of a moat to greatly reduce competitive pressures, and so should be subjected to different standards than a local bar or paper -- and if the analogy is to a newspaper, then Twitter should be treated as a publisher with all the attendant regulatory baggage that carries. It's hard for them to argue they have a right, as a private company, to shape the conversation, and in the same breath claim they're shielded from legal responsibility for what takes place on their site.

It's definitely a tricky debate, but in my personal value stack I place individuals' freedom of speech much higher than a private company's right to refuse service, so that's where I fall.