I see. My only criticism of it would be in some heated debate scenario. Where a conversation started really ugly, but eventually became a teaching moment (as much as I hate that phrase). A lot of respect could potentially be earned by the people for resolving their differences. A throwaway could make this less achievable as people gravitate to it for protection. Then again, if the catalyst for such a conversation can only be garnered through the throwaway in the first place - it could be a good addition. I'm all for an experiment though and love the idea that it is one shared mask.
I believe that if people are mature enough to resolve their differences through reasoned discussion that they are not the type of people who would resort to an anonymous bashing through a shadowy account. However, just today I had a discussion with someone who was not anonymous who I think is very rude and does not do their own arguments justice due to the way in which they present them. Anonymity does not guarantee venom, nor does reputation always prevent it.