[Sophira]

Perhaps if JavaScript did not exist, those apps would be using something separate to the Web, and the Web would have remained a mostly non-interactive, read-only medium.

You're overestimating the importance of JavaScript here. phpBB didn't start using JavaScript until phpBB2 was released, and I believe that UBB, the forum software phpBB was based on, didn't use JavaScript either at the time. (Of course, this was partially because JavaScript was so limited back then.)

[Silhouette]

OK, but forum software on the level you're talking about was near the pinnacle of social networking sites at the time, and seems almost prehistoric by modern standards. The kind of slick interfaces and near real-time feedback that users enjoy and expect on today's forums can't be done the same way, so instead JS is widely used both for simple things like collapsible discussion threads and for more sophisticated interactions like live previews when typing comments with formatting.

A case in point: I'm typing this on HN, which is a forum I read often and enjoy for its content and for the interactions with fellow contributors. However, the interface to HN is unquestionably less efficient than the interface to Reddit, which offers similar functionality but without limitations like needing to open a new page that only shows the immediate parent comment when replying to something.