My current position on capital punishment is something like this:
Capital punishment is ethical and just in principle.
However, no justice system is perfect in implementation. If we set out to do the right thing and execute certain criminals, we are certain to sometimes do the wrong thing and execute an innocent man.
Therefore, perhaps we should refrain from doing something so drastic as executing people, because the risk of killing an innocent person is greater than the reward of seeing justice done.
However, we deal with this risk-reward conundrum at all scales in the justice system already. An innocent man can be released from prison after ten years, but he'll never get those ten years back. He'll never be without the experience of ten years of prison life. He'll probably never fully recover his lost reputation, his lost income, etc. Maybe, like Job, he'll bounce back and ascend to even greater heights, but even that will never make him whole from the curse of injustice that was placed upon him.
We don't say, "we should abolish life sentences because the risk of sentencing an innocent man is too great, and the loss of years of life is irrevocable and unremediable." Instead, we say that we should reform the justice system and reduce the risk of incarcerating an innocent man to some acceptable level.
I think we all agree - whether we admit it or not - that some sort of justice system is necessary to the function of a healthy society, and that we must accept that sometimes an innocent man will be caught in the net.
Therefore, perhaps the remedy for capital punishment is not to abolish it, but to reform the system that feeds death row, and get an acceptable balance between the risk of executing an innocent man, and the reward of seeing justice done as far as practical.
But I don't know for sure either way.
On the other hand, I think that if we do intend to execute criminals, the method should be relatively quick and painless, but also practical and cost-effective. No method is going to be perfect every time. Shooting, hanging, electrocution, injection... all of these are bound to be awkward and uncomfortable to some degree. All of these are bound to go horribly wrong from time to time. If we're going to do it at all, it's incumbent on us to mitigate these risks. But I think it's also incumbent on us to recognize that these risks are not entirely avoidable, and that some distress or discomfort in the convict's dying moments is a small price to pay for seeing justice done.
---
All of this assumes that you and I are more or less on the same page, about the concept of seeing justice done. If we're not, you're probably going to think I'm some sort of horrible monster for even daring to discuss the issue as I have.