Defederating would pretty much cut off a lot of potential new users that want to see posts on Threads while also not wanting to have a Meta account and all the issues that come with it.
Kinda the point, no? Kill Threads in the cradle by denying it access to the fediverse.
I would have phrased it as “supporting” Threads. If you don’t defederate, Threads will take over your instance. Either directly through the sheer amount of posts, or indirectly by colluding with your instance admins. Or both. It’s how they operate. And then the ads and data harvesting and walled gardens will come.