There’s a lot of reactionary anti-corpo types here. There’s really no good reason for users to want to defederate from a Facebook owned instance. It’s also a pointless stance, as threads is a Twitter/mastodon style site and not really compatible with reddit/lemmy style sites.
There are some technical reasons to avoid federating for those hosting instances. The software forces local copies of everything users subscribe to which is a massive space concern. There’s also a problem with performance of syncing that data for large instances that’s already a problem with .world size instances, where it can take a day+ to process new comments.
That’s a reson to not subscribe or participate, not defederate.