More generally, I personally prefer having separate user accounts on each website I use, so that if one account is compromised the others are still fine. If I use my Google log-in for everything, and it is accessed by a third party, my online security is totally down the pan across the board. However, because my actual strategy is to have a separate password for each website and then use 1Password to keep track of them automatically, the vulnerable point is 1Password, which isn’t available unless you have access to my machine (and also can’t be given away by phishing scams and the like).

I understand the drive for global log-ins but not providing a separate log-in for those who don’t want to connect all the dots in this way seems shortsighted to me.