Some would-be users have already been booted off the network for using an identifier that, in Google's judgement, does not qualify.
"By providing your common name, you will be assisting all people you know in finding and creating a connection with the right person online," the company says.
That reasoning falls at the first fence; most people who relate to me in a journalistic context call me Stephen (that's my byline); family and friends almost universally call me Steve. Google+ makes a feature of the ability to maintain distinct "circles" of relationships as we do in life, then ironically denies this with its naming policy.
As senior editor at The Atlantic magazine, Alexis Madrigal, put it, in a recent widely-tweeted article: "the kind of naming policy that Facebook and Google+ have is actually a radical departure from the way identity and speech interact in the real world. They attach identity more strongly to every act of online speech than almost any real world situation does."
The New Zealand government's Identity Verification System (IVS), part of igovt, preserves a consistent "identity credential", but still allows people to log on with different names to different agencies.