defederating meta would only hurt those that defederated
That's a bit too simplistic. Defederation has many consequences, some subtle. It depends on personal preferences wether the sum is beneficial. Specifically, some people see it as an advantage to not see content coming from Threads, and not share theirs with Threads.
way more users than people here think will want to see and manage Threads
I'm doubtful, but maybe. We don't have numbers on this.
We also don't need to reach a consensus. Maybe there is demand for instances which are defederated and demand for instances which are federated. People can choose where to have an account (which includes the option to have more than one account), people can try to inform themselves about an instance's policy, and they can try to influence an instance. This is all fine, fediverse working as intended.