This is a terrifying way to destroy an online community if a person floods it with nonsense content like this.
In a few years, the standard Silicon Valley “Growth Hacking” job description will include using AI to deploy fake content to your competitors’ sites, destroying their user community.
Nonsense flooding will make it more difficult for people to establish their identities on a network, but once it's established, they'll be in the clear. If someone has to pay to have their first thread or two reviewed, it will take serious money to flood a site to death.
(A similar solution to email spam has been waiting to happen for decades -- charge a fraction of a penny per email, and nobody is harmed but spammers. Maybe allow exceptions for officially recognized organizations that have to send a lot of messages, like political campaigns.)
This would be even better: Email recipients grant free access to whoever they want. A tiny price would be charged only when sending to someone who has not granted such access.
Unfortunately, even though snail mail has associated costs I still get a ton of junk.