I disagree with the object level of this quote. Censorship can achieve multiple goals, and a lack of censorship does not necessarily imply "a regime of robust discussion."

Examples of the first would be using the censorship itself as the action (e.g. a despot censoring religious minorities doesn't just limit discussion, it's an active method of subjugation), or protecting people from messages with annoying content or form (e.g. regulations on advertising).

The second is nearly a human universal, but is especially clear in propaganda situations - if we're at war, and someone is spreading slanderous enemy propaganda, and I destroy their materials and arrest them, this is censorship. But it also increases the robustness of discussion, because they were trying to inject falsehoods into the discussion. Or for another example - sometimes you have to ban trolls from your message board.

I also dislike the implications of this quote for any discussion where it shows up. Some times ad hominem arguments are right. But they're almost never productive, especially when cast in such general terms.