Honestly I think this is good for the fediverse.
It instantly boosts mastodon and Pixelfed’s reach, which means people won’t dismiss posting there as it never gets seen.
I would never open a Threads account, but it unlocks seeing content from a lot of people I like who ditched Twitter but didn’t understand mastodon.
Yes, this can also be Embrace, Extend Extinguish, but I’m happy for the publicity.
If people don’t like it they can join an instance that defederatrs from Meta and that’s totally fine.