Original Idea by Midnight:

"You know what sucks? Getting killed by a fellow innocent. You know what really sucks? RDMers. Wouldn't it be great if there was some kind of system to stop this? Well I think I have hit the jack pot. What about a karma system where the more innocents you kill as an innocent makes you more susceptible to damage. Not by too much since this would carry between rounds but enough so that constant mistakes would leave you at a disadvantage. However when you kill a traitor your susceptibility decreases, allowing you to take more damage. Each traitor killed is equal to say 5 innocents killed. Also when your a traitor your susceptibility is reset for that round only. Since the system relies on damage there would be no way to know who is a traitor or not. I mean if someone shot you just to check if you were a traitor you would have grounds to shoot them back. So what do you think?"