So basically 1 in 20 inmates on death row are innocent, and people (mostly conservatives) are A-OK with that percentage of innocent people being subject to state-sanctioned murder in a very brutal way that's far from painless. A dog being put down by a vet receives more humane treatment than a human being put down by the state.
That "at least 4%" bit makes that even worse. Just look at the List of miscarriage of justice cases on Wikipedia, it's not not exhaustive and it's huge, I cannot morally or ethically justify capital punishment on that alone, the whole state-sanctioned murder bit just makes it even more horrific.
So everyone that punishes someone with death will receive the death penalty?
Of course, you will have to punish the person that punishes the person that punishes someone with the death penalty with the death penalty with the death penalty
But then, because they punished someone that punished someone that punished someone that punished someone with death with death with death with death, they will have to be killed
Eventually, you will run out of people who can punish someone with the death penalty, so you will have to do it. Since you killed someone as a punishment, someone will also have to kill you, but because you are the only person that can do that, you will have to do it, ending the loop