I have several reasons for not supporting the death penalty. The possibility that we might accidentally kill even ONE innocent person is enough to give me pause...but there are other reasons to consider.
1. Citizens tend to internalize the morality that is embodied in the laws of the State. Hence, if the government uses killing as a solution to problems, people in a general way accept that killing people is also an answer to their own problems. Macro level policies have a way of being reflected in the microcosms within.
2. Laws change too fast. Legal reasons for killing may seem clear now, but suppose our government was out of control? What if laws were passed and changed so quickly that the government suddenly allowed itself to kill citizens for any number of reasons, without trial, in other countries, or without the knowledge of the populace at large? The power to kill for political reasons is a very dangerous slippery slope, and especially tempting for those drunk with power looking to move their own agendas forward.
3. There is no evidence that the death penalty acts as a true deterrent. In fact, statistics bear out the opposite effect. For this reason, killing people as a punishment seems ineffectual and unnecessary. deathpenaltyinfo.org/deterrence-states-without-death-p...wer-murder-rates
I believe the study linked in the initial question, and because of the reasons I expressed above, I do not support the Death Penalty.