I think Facebook is an example of a service that has - you use an email & password to log in, but your name is what is displayed everywhere. But Facebook has m

I think Facebook is an example of a service that has - you use an email & password to log in, but your name is what is displayed everywhere. But Facebook has made other trade-offs that people might not always agree with: it requires people to use their "real name", and while this policy is sporadically enforced, they probably have checks for people cycling through names, and they also focus on communicating with your close social circle where there is less incentive/opportunity to impersonate people. Twitter has something in between where you can have a handle, which must be unique, as well as a display name, which does not. Without a unique handle @handle isn't a thing that works. You could do something like Facebook and have someone type @<Display Name> and provide some drop down for disambiguating, but given the wide open nature of Twitter, this seems more abuse-prone. Identity is still hard to manage online, and I don't think we're really ever going to solve the problem in a way that makes everyone happy.