I’m old enough to have had one and a Tripod and Prodigy page for that matter. I still don’t think the analogy holds up at all. Geocities was a single centralized commercial entity even. People contributed the content and they hosted it, this is still to this very day what traditional web hosting is. What I guess you want is more authentic, personal content?
If AI content is a chief concern, what would be the mechanism to stop the flow of it that couldn’t be applied (at a technical level) to the internet as it exists today? Or what human-driven policies could be made and policed better on a new network that nobody truly owns? (hint: this is already the internet)
Ad revenue while it does convert free-service users to dollars isn’t the only means of commercialization (traditional business subscriber models for one) and as long as any financial incentives are there (not just ad-related), there will be spam of all kinds. Any general purpose medium will be come subject to this, it’s inevitable.
To the large point, a very very small amount of users have the means, capability or desire to host their own networks and services. Raising the technical bar means lowering the audience size. Even then, you’ll still find bad actors and people you don’t agree with.