It's not just that there is a risk of re-centralization from network effects. Since you mentioned email, there is also a large risk that filtering unwanted con

It's not just that there is a risk of re-centralization from network effects. Since you mentioned email, there is also a large risk that filtering unwanted content and impersonators from appearing on your instance becomes so expensive and/or time-consuming that only a few instances have the resources to do it, just like happened with email.