Some non privacy considerations:
- mod workload increasing to unsustainable levels with the overnight addition of millions of users
- meta would be a large enough instance to be considered a monopoly of the entire fediverse
- the fediverse goal of putting control of social media back in the hands of users would no longer be possible if companies controlled the majority of the space
Most people probably didn't consider the internet something that could be monopolised at the start either.
We have the same view on private social media.
IMO we should treat this like any other instance that goes against what we want to see on the fediverse, defed it on all the main instances and if someone wants to access it they can have a threads account or an account on a small instance that is federated with them.