You do not have to carry all newsgroups, and the last time I used a free Usenet node they explicitly did not carry any binaries (too much traffic and too much liability). The reason nobody uses Usenet is that unmoderated newsgroups were taken over by nazis and trolls, and moderated newsgroups have no particular advantage over forums as far as "free speech" goes.

(Though I take issue with the idea that moderation somehow implies less free speech. It is hard to express an idea when you are buried under a pile of off-topic trolling and nazi conspiracy theories.)

> The reason nobody uses Usenet is that unmoderated newsgroups were taken over by nazis and trolls

Some of the sci.* hierachy was taken over by the mentally ill and crackpots. They aren't hateful or intentionally trolling with their insistent claims that they have discovered free energy, come up with new insights into the evolution of human language, etc., but the effect on fruitful discussion was much the same.

At some point, trolling becomes indistinguishable from mental illness and crackpottery.

only in sufficiently advanced civilizations.

Moderated forums and moderated Usenet groups both have the characteristic of not being subject to the whims of a central platform. Contrast Facebook groups and subreddits.

Except for alt.hackers. It was a moderated newsgroup but there was no moderator. How do you post? That was the point. It was a fun group.