@aral @Gargron its a tough one..
For me personally the primary reason to defederate threads is history - for decades large corpos have followed agressive assimilation principle. There are barely any exceptions and I cant come up with any, its highly likely threads will be such a case again.

On the other hand, federating with threads gives access to millions of new users that can be positively influenced, threads brings with it potential to take fedi out of fringe and into mainstream.