Not sure I entirely agree with that either. Scientific debate is evolving with the times. Online isn't a traditional formal venue where these debates happen, but they do happen here too. Scientists discussing actual scientific facts, or disputing each other's claims get silenced too. Seems like a reasonable interpretation of "scientific debate".

And I suspect the OP meant "scientific debate" as the public's discussion of science and the policies that should be formed around the facts as they see them.