You assume due process is uniformly applied in all death penalty cases, which has been repeatedly shown to be false in America. I suggest Googling "death penalty lawyer asleep" as a good starting point for this topic.

I didn't assume that; what you seem to assume is that death penalty cases more often lack due process than other cases. You may well be right (I have no idea), but that would still only be a weak argument against the death penalty and a strong argument for ensuring due process.

I suppose what makes the death penalty different is that you can't fix injustice after the fact. Once it's carried out, it doesn't matter whether the verdict is overturned.