At the moment, Threads runs from one domain. Do you seriously think it’s going to stay that way? They also have 100 million users, compared to less than 2 million across the entire fediverse. Once Threads gets serious about federation - maybe a year or two from now - what you’re suggesting is going to be like constant whack-a-mole. That’s in no way a fun prospect.
And even if they stick with one domain (which they won’t) - the hate groups on Threads will still be producing content that other fediverse users will be talking about/linking to/quoting etc. The fediverse is very quickly going to become a miserable place to be for those who thought they had found a place where they could be free of all that harassment.