The thing about a single online Identity is that there should be no way for it to be revoked against the will of the person it identifies. In real life I am who I am, and unless I choose to change that, no-one can legally take my identity from me.
There's been too many horror stories of people being locked out of their Google or Facebook accounts by Google and Facebook, even for the most minor of infractions, and that person immediately also losing access to to all the other services they used 'Sign in with...'
Until this problem is solved, I will never switch to a single online Identity for access, and I certainly will never use my Google or Facebook account to register with third party services.
There's been too many horror stories of people being locked out of their Google or Facebook accounts by Google and Facebook, even for the most minor of infractions, and that person immediately also losing access to to all the other services they used 'Sign in with...'
Until this problem is solved, I will never switch to a single online Identity for access, and I certainly will never use my Google or Facebook account to register with third party services.