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.
Blocking instances has been standard practice for ages on mastodon, it's an important moderation tool to keep radical right-wing instances at bay. Without it, the overall experience would be much worse. Of course there will always be a debate about which instances should be defederated and which shouldn't, but as another commenter already mentioned, everyone will be able to make their choice and find their own little corner.