Embrace, extend, extinguish. Something that has been used by large companies in the past to push out the smaller, more open systems many times.
That said, I agree with @[email protected] that blocking by default would be against the open platform that we claim we want. Users can choose to block accounts themselves or not interact with Threads. So long as these instances are publicly available, there's nothing stopping big companies from hovering up the data passing through them whether or not they are attached as a peer.
Those are the two main points that I've seen as possible concerns with allow federation with Meta or any other commercial property and neither is really that severe.
The good side is that, for folks who are only ever going to go with a big company's site, it still allows us more privacy-minded folks the chance to interact with them. Something that is just flat out impossible today without compromising our own principles.
Yeah, it’s a complex topic with no clear “right way”. That’s why the major social networks have always had trouble finding a method that works and there’s always some group who feels oppressed and/or marginalized.