If registered users can just log out and act out their aggressive impulses using an unregistered account, I don't think anything else we do will matter (including imposing moderation). Also, you're focusing too much on the straw that broke the camel's back. This is just the latest conflagration resulting from an underlying pattern of behavior, which unregistered accounts contributed to.
Regardless, community building requires asking for a degree of commitment. If people just want a question answered, there's other places for that. I would personally prefer a friendly environment for discussion, rather than a simple Q&A hub.