The issue is that this does affect Kbin because Kbin is a microblogging platform. It's also a thread aggregator, but it has microblog functionality that some people do actually use. Should we not defederate, stuff from Threads will flood the microblogs of Kbin. If your home page is set to use the All Content feed (like mine is), you'll see microblogs from Threads there. This doesn't have as much of an effect as it does on a purely microblogging-focused platform like Mastodon, but it does still affect a big way that Kbin is used.