I don't think you'd even have to ban for-profits. If someone wants to run a niche forum and try to make a small business around it there's nothing wrong with that.
https://diysolarforum.com comes to mind, Will runs a related informational site and YouTube channel. I don't know if he technically made a business for it but he could have, and if it continued to grow there could be good reason to hire a few employees.
I think the real difference between social media and forums is the algorithmic feed. We could likely codify a ban on algorithmic feeds of user generated content. That would go a long way and would be much easier to spell out in a law than a targeted ban on advertising, social media use by age, or certain types of business models.
https://diysolarforum.com comes to mind, Will runs a related informational site and YouTube channel. I don't know if he technically made a business for it but he could have, and if it continued to grow there could be good reason to hire a few employees.
I think the real difference between social media and forums is the algorithmic feed. We could likely codify a ban on algorithmic feeds of user generated content. That would go a long way and would be much easier to spell out in a law than a targeted ban on advertising, social media use by age, or certain types of business models.