Great feedback. This is a discussion we've had many times both internally and externally. I'd like to share some perspectives from inside the product team here. To us the core issue is not whether we should allow anonymous posting, but how we can minimize friction to customers sharing their feedback. Anonymous posting is one solution to the challenge, but very problematic one as has been discussed.
As a datapoint, we launched a feature on our blog last year that allowed for anonymous sharing of ideas, and out of almost 400 submissions, exactly 3 were intelligible. Most were spam. We finally disabled it.
By contrast, when users send us suggestions via email they are not anonymous. Their email represents a unique identifier, and the attached data often indicates their real name. So a desire for true anonymity isn't really the issue.
It is quite clear that no one wants to create a new account if at all possible. This creates friction. We've rolled out various features to reduce blockers to use, such as single sign-on and one-click login through social systems like Facebook, Twitter and Google. We are currently looking at ways to put these one-click options front-and-center (they're a bit marginalized at the moment). While this won't be a solution for 100% of everyone, in our estimation it is a more durable solution to the friction problem. And it makes it even more difficult for spammers to waste your time.
We're certainly open to other ideas to the core challenge. Thanks for sharing!