Personally, I'm of the mindset that there are situations where the death penalty seems reasonable. I think there's been a lot of abuse of it, and people use it as a quick way to feel better about victimization. There's surely many cases where even the families of victims have regretted calling for and then getting the blood of someone. Then, as has been mentioned, there's always the risk of judging someone wrongly and without a doubt taking what isn't ours.
I suppose I'm okay with leaving it up to the state. That seems the most fair.