I do not want my posts from anywhere on the Fediverse on FaceBook.
I have have seen people express worry over FaceBook posts showing up on the Fediverse. But, what about our posts showing up on FaceBook.
If Meta federates with the Fediverse, do my Mastodon posts (e.g.) show up on FaceBook?
If the instance you are on doesn’t defederate from this hypothetical Meta instance, then yes. I’d leave any instance that didn’t immediately do so upon it becoming a thing, personally.