@smallpatatas
I don’t understand why you need to "convince" anyone. If you want to block Meta you can just block Meta or join an instance that blocks Meta, there is no need to collectively defederate.
If your instance’s admin has enabled SECURE_FETCH and you block Meta’s domain (even as a simple user) you are effectively isolated from meta, even boosting your posts can’t expose them to Meta (thanks to SECURE_FETCH).
This can be a personal decision it doesn’t have to be collective.