My solution to the problem 
@jwz mentions:
1. Make password the •only• login field. No username/email! Just password, and you’re in!
2. Because they now identify users, passwords must to be unique across all users in a system.
3. For security reasons, require passwords to be unique across all sites on the entire Internet. A password can be used at most once in human history.
4. This renders account recovery impossible in many cases.
5. Over time, users are thus able to use fewer and fewer sites, eventually being forced offline altogether.