I don't think it's going to be "singular bad actors" in this case. I think it's going to be every server owner realizing why the situation became what it is on Facebook, Instagram, Twitter, and Reddit. When operating and development costs stretch beyond the grasp of donations, when the number of users far outstretches the number of donors and customers, server owners will have to seek out ways to monetize users. So, sure, you'll have people who are willing to put in the investment to launch their own server and federate as they see fit, rather than pay for the service. But you'll have a lot more people who are unwilling to pay.
That means ads and paid content. That means login walls and paywalled content, "premium" access and features, etc. I expect that every large Fediverse server will end up that way. Either that or the way they'll stay ad-free is to kick off the users and keep only the paying customers (these people will be called "donors" so they don't expect any benefit for their money). After all, kicking a user out of one instance of the Fediverse doesn't have the impact that it does on Reddit. Heck, kicking a thousand out doesn't. There's every other instance's customers and users still to talk with. There's always the ability for those people to invest in the platform with their own instance, or join one with a smaller number of allowed (non-paying) users.