It's fine if single instances do consent-based federation that prioritize safety over openess, but why should it become the default for all instances? It will result in instance protectionism and an overall decline in discussion quality. Making it opt-in means people will connect less likely with folks from other instances, meaning people will mainly stay on their instances, meaning it supports tribalism in the Fediverse. More safety usually comes at a cost, too. In this case: less interaction with other instances.

But if you federate with instances that you trust good enough in the first place, constent-based federation is not necessary imo.