Unbalanced Vision

My supervisor and I were discussing about scaffolds, and out of the blue he asked me if I supported death penalties. He asked me if my country can take my life. I said 'yes'.
"Rachel, you see, my country cannot take mine."
"But human beings can go to extremes and do horrible things."
"But what if they are innocent? You see, that is Barbarianism."
The Life of David Gale is about capital punishment, and I still don't know what to make of this system. All I know is that in life, the margin for error is so little... And what is the force that keeps us sane?