I believe Google's stated reasons for insisting on this may be different from their actual reasons. Google isn't doing this to protect their users, they're doing it to protect their revenue.

Google Plus is a "free" service. Which inevitably means that the users are the product being sold to advertisers and others. And a user's legal name—which can be linked easily enough to their address, etc—is a very valuable asset indeed.

So all the arguments in the world refuting their stated reasons are not going to make even a tiny dent in their policies.