Would defederating make things worse? I would want to see posts from these users and blocking them would force users to use Meta's app and in turn more likely for users to switch over and create accounts on their app.
I understand its a big scary corporate business but the fedaverse should be open. Closing off a potential big userbase does not seem to be the smartest move and it opens up the rabithole of instances starting to block each other left and right, ruining the entire point.