The ability to ban rogue users would likely have helped them immensely. An invitation-only system would probably have been of benefit as well.

Nothing is foolproof, obviously, but their users were working quickly. They only would have needed to keep malicious users away for a limited time in order to achieve success.

The author likely doesn't have much real-world experience with users or his team would have built this sort of capability into the software from the ground up. Any dev worth his or her salt knows to never trust any user.