If I go to join Google+ then I am almost certainly doing so with an existing Google Account - and that account may well already be full of things that I do not want to be connected to my public identity.
The two use conditions may well have looked similar from inside Google, but they are most definitely being felt differently outside of the company.
And that's why Facebook gets very little in the way of complaining about their (nigh-identical) policy, and Google are taking a lot of flak over it.
I really do think that unless they back down on this it's going to be the death of the system.
Original post on Dreamwidth - there are comments there.