I find interesting that you in the US are thinking in banning the death penalty.
Here in Colombia death penalty was banned about a century ago, unfortunately, it has done more harm than good, because criminals (even very bad ones, the kid rapists and stuff) are not scared of prison, prisons are so crowded that sentences are short (https://en.wikipedia.org/wiki/Luis_Garavito is a good example, I don't think a lifetime of prison would forgive all he did, he should be condemned for 1800 years) and this has led to crime rise.
There is a common belief that politicians banned death penalty long ago to be able to be corrupt without any risk, in the long run if they're not dying, they could steal a lot of money and then use half of it to get out of prison early.
I know US corruption is not as bad as Colombian corruption. Unfortunately we have to deal with our system, and the ban of death penalty has kept terrible people in our country for a long time. It may be unethical to kill someone, but in the end is the lesser evil, because it will never compare to the harm that this person does to the society. As a Colombian I feel that corruption and crime is going down now, and we are proud for it, but I also feel that if we took the 'evil' decision earlier, we would be much better now.