The difference between censorship and moderation is the ability to realistically opt-out. Your friends might get mad at your for saying something, but you can choose your friends. Your community might not allow certain speech, but you generally get to choose the communities you are a part of. When the avenues where 99% of all communication go through "moderate" speech a certain way, that starts being censorship.

The difference is somewhat part who is doing the moderating, but it is far more important the ability to opt-out without significant negative impact.

Of course you can have online discussion without moderation. In the most basic form: you publish on your site, I respond on mine. No moderator involved

And there are plenty of other differences besides "who", for example, "how".

> Only difference is who is doing the censoring.

It's a universe-sized difference though. If a platform owner is doing it you can somply go to another platform. If a democratically elected goverment is doing it you can change the government though it's much harder. Or at least you can soothe yourself that it's being done for the benefit if the people as "the people" sees it. And if an authoritarian government is doing it, you are screwed.

as long as it's not the government who is doing the censorship / content moderation then I'm OK

since the government is too powerful and can enforce its ideas with legal violence

uh maybe you can't