Recently I have a harsh experience with my AWS account. I made a dumb thing, my email inbox is registered under a domain, and somehow my domain's MX record is gone and I can not receive email from AWS to authenticate to the right account to fix that MX record. So I am permanently banned away from that account due to the policy of AWS

Quite silly, yes. At the same time, I do think this scenario can represent a possibility when people need to rely on only one way to authenticate their entry. That is really frustrating when you make dumb thing under this circumstance.