Surely, in a conversation, the most damaging thing you can do to the integrity of that conversation is to selectively nullify the voice of a participant.
It ceases to be a conversation then. It is something else, posing as a conversation.
Maybe it would be better if this censorship-power is democratically controlled. But if this power is given to an individual. Well that's different.
In order to have a conversation at all, you need to deal with the guy with the megaphone first. If you do not have moderation, you drown in spam, and do not have a conversation at all.
It ceases to be a conversation then. It is something else, posing as a conversation.
Maybe it would be better if this censorship-power is democratically controlled. But if this power is given to an individual. Well that's different.