What would be the problem if Threads federated with Lemmy&co in the future?

I’ve seen a lot of comments suggesting Threads should be pre-emptively defederated by Lemmy/kbin instances if it tries to join us. I’m a bit confused what the problem would be. When Meta does its usual corporate bullshit over at Threads, how would that hurt a user or community based on Lemmy.world? If anything, wouldn’t it...