An idea mostly doomed to failure, the vast majority of people (that are viewing the ads paying for the service) don't want do deal with that bullshit.
Moderation is a hard problem. You first have the flood/spam attacks that unless instantly dealt with will bring a service to its knees as there will be hundreds of bad messages for every good message creating an enormous bandwidth and filtering cost for each user.
Then there is a the porn problem. Any place that doesn't instantly block porn will be flooded with porn.
Then there is the flood of off topic bullshit that shows up in any given channel.
And from that point there is 20+ other little things that make people feel welcome and want to come to a channel in the first place.
Simply put anyone could have created and open protocol social media. No one has because it's hard and fraught with problems that your users won't want to deal with.
Think of it as a filter. Reddit is a filter on a walled-in social network. What you post there isn’t visible on any other social network and vice versa. But because of that lock-in you are limited to whatever crappy moderation one specific front-end sticks you with, with no alternative if you still want to interact with that social network.
- spam is now too expensive to bother. Free x infinite is free. $1 now means spam costs thousands to try and uphold. Not worth low effort content
- Rule enforcement is much more tenable now because ban evasion has a cost. Is someone really going to pay $1 each time to try and post some porn or whatever else? 99.9% won't. That will give a feedback look where the community overall should get easier to moderate as it grows, not harder
- Needing to pay menas you also have a community that at least skews in the adult age. Kids don't/won't have easy access to a credit card for even a $1 payment.
The main problem is still the same as free platforms, though: network effects are very strong. Adding more hoops will make adoption harder, and that's arguably the hardest part of a new platofrm.
These companies burn through VC money to build systems with network effects then turn around and effectively extract rent. Rent extraction is economically parasitic and anti-productive. This is exactly the sort of thing the government should address by mandating open protocols.