This seems like a flippant insubstantial criticism. Facebook is one of many many options—including first-party username+password auth. It's more like, "Welcome

This seems like a flippant insubstantial criticism. Facebook is one of many many options—including first-party username+password auth. It's more like, "Welcome to our federated decentralized service. You can log in with your Facebook account if you want to." Which doesn't sound like a bad thing to me. More choices for users is usually a good thing. If users' choices have bad consequences, that's not Matrix's fault. Though maybe Matrix should warn people that if 3rd-party cuts them off they'll be locked out of their Facebook account too—choices need to be informed!