To be clear, I want it to be users deciding on Lemmy too. Also, people already here moving to threads wouldn't be the problem, we're small in comparison to them. It would be a few things:

They would bring in a huge party of users that would take it over and overwhelm the current users. It would be like a cruise ship of tourists taking over a small town and breaking everything for the current residents.
They could post to Lemmy, but we can't really post to Mastodon. They're going to send ads our way disguised as content, guaranteed.
If they can manipulate the users from Mastodon, it's going to get out of hand fast. They have teams of devs and psych engineering to accomplish that.
This is volunteer ran, do we have enough energy to fight Meta when they try to enforce something?
Can they manipulate Activity Pub software because we're a small team of devs? If they can, they will.
One person mentioned them having instance owners sign NDAs. What's up with that?

[–] neshura@bookwormstory.social 2 points 11 months ago

If they are having instance owners sign NDA's they must have pre-selected who to talk to or only target Mastodon because feddit.de just pre-emptively defederated threads.net after users made the owner aware of the news and it's one of the largest instances (even more so if you go by MAU which is arguably what Meta would be intersted in).