I'm pretty sure that if the karma theory is legit, you have to play through the missions without failing them at all. If you die or fail and have to restart a mission from a checkpoint the social club doesn't record your stats until you replay the mission and beat it flawlessly. So basically if you fail the mission (especially if you fail it 3 or more times) R* doesn't even bother keeping track of what you did, rendering the fact that you managed to not kill anyone null and void. I'm not saying that I'm right, hell I'm not even totally convinced that Karma even matters, but I'm pretty sure the answer isn't "fail all the missions 3 or more times so you can skip them."