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.)