I don't think that G+ was a mistake. The only real issue is the real name policy, though I fail to see how they'd be able to enforce it. People could create alternate email addresses with fake names (and some did), and use it when they want to participate social "i-events" without giving up their id. It's been like that before G+, and it would only take a small move from them to correct it. Of course, the downside of…
Which is really daft, considering that the whole 'Circles' thing was initially designed to do away with the 'different content for different audiences' issue originally.