Any centralized identity system solves a problem we don't have. It doesn't simply serve to identify a person. It serves to aggregate an identity and tie together extremely disparate and unrelated data. It enables a data leak or abuse to not just compromise one service, but all of them at once. If there is a leak of data from, say, a dating site that involves dumping the public keys of the users alongside the user activity associated with it, then the credit card company and electric company and water company and the gaming forum you signed up for and multitudes of other utterly unrelated organizations now have the ability to correlate your dating activity with your activity on their service. The identities on all of those separate systems being the same identity is the problem a centralized system solves. And it's a problem we have never had.