Going unremarked in this nostalgia is that those old forums were still moderated, sometimes heavily, and the #1 tool was the ban hammer. It was not a free speech love-in. Hell, Something Awful would automatically replace your post with "yams" if you merely hit a trigger word, if you weren't ejected outright.
This is an interesting point. But being banned from a small forum feels like disassociation. Being banned from a huge central platform—the de facto public square—feels a lot less like free speech.
Maybe a better way of thinking about this is that “free speech” on the Internet is about decentralization of small communities even if many of those communities themselves skew authoritarian? If you are banned from a small private gathering, everyone’s practical speech rights remain in-tact. You aren’t banned from the larger system.
Bringing up moderation is a good point. But, it isn't so simple.
Moderation isn't something that's changed. Forums and modern social media both moderate. They do it to varying degrees.
Social media moderation comes in multiple forms. First they will choose which posts people see in their feed. This is a form of moderation. It's easy to have topics and even people just not show up. What shows up is based around engagement and money.
There is also moderation about content. People can be labeled or removed from visibility.
Then there is banning where banning isn't on the topic but the whole system. And the systems are tied to other things (e.g., banning on FB impacts your Oculus ownership).
Old school forums were based on topics and were different systems. They were moderated, if they were, for that system. The moderation was typically around content you posted. They didn't control the flow or order you saw it in. It was the content.
When banning came up, it was just for that form. So, if someone is banned from a jeep owners forum they are just fine interacting in a forum on web design.
I say this to note that the way the technology is developed has an impact on the way people act.
For example, these days there are people who don't want to speak out on some topics because they are fearful they will be banned or negatively impacted globally.
I'm not suggesting how the technology should be built. I'm trying to point out how the system design impacts the way people think and behave. Older systems were designed differently and had a different impact. It's worth noting these things.
