To prevent mob egging, a Stack Overflow approach might be helpful: make voting down to cost karma. Unfortunately this works better on Stack Overflow as upvotes

To prevent mob egging, a Stack Overflow approach might be helpful: make voting down to cost karma. Unfortunately this works better on Stack Overflow as upvotes give you either 5 (on submissions) or 10 (on comments) karma while voting down only costs you 1 karma.