Unverified usernames do not inevitably result in a site that is overrun by spam. Time-tested methods of downvoting, flagging, reporting, and semi-automated filtering can quickly dispatch such shell accounts. You only need to look to reddit for proof of this--a site where users sometimes employ their username as the punchline to the joke. That's right, a username can be an avenue of communication in itself that carries positive, non-spammy (and dare I say fun?) results. Another example: would @shitmydadsays have caught on fire the way it did if the account was named +Justin Halpern instead? I doubt it. The final obvious example: HN, which thankfully does not require "verified" identities.
When I read discourses from Google like the OP's it reminds me how right moot is when he says that creativity is only preserved in a culture that values privacy and anonymity. When everybody is permanently attached to every action, nobody bothers to test the norms, and all that's left is consumption of "safe" content from centralized producers. Of course that's what Google and Facebook, being glorified advertising networks, actually want. Your anonymous account has no money to buy anything, no predictable real-world holdings or credit score or behavior, and therefore no value to an advertiser.