

As lemmy is federated, nations/groups/blocs/whatever, can come up with their own system or adopt this system. What matters is who (instances or even end users) is recognizing the identity provider’s authority and willingless to ensure each person has just one identity.
If I am convinced your local ML group is making a good job ensuring everybody just registers once, I can display this along with the message.
In principle, true, but if this happens at scale, it will be detectable (not by our protocol, but outside of it) and a state has a much bigger problem if people (other states) lose trust in their IDs.