You'll find that many people are very reluctant to give up that sort of information about themselves though, whether it be for privacy or because they don't like being incessantly spammed. I understand it existing as an option, maybe even a default, but to make it to the only method of authentication seems insane. Sure, many users will deem that the benefit of using the application overwhelms any negative implications, but it would be nicer if they weren't forced to make that tradeoff in the first place.

I'm not against the option existing, I'm against it being the only option.