Random musings about the death penalty

So I'm not really in favor of the death penalty, for a number of reasons.
What strikes me, when I think about it, is that we have an odd way of going through with the death penalty. We're supposed to avoid cruel and unusual punishment, so we kill people by gassing them, injecting them, hanging, and firing squad. None of those seem very humane. The injection comes the closest, but of course, the regulations are based on vet guidelines, so who knows how effective and humane it is for people. Seems to me that the most humane way would be a nice sharp guillotine. Quick, clean, certain death. No scorch marks, no abrupt defecation, no silent suffering, no death by slow bleeding or multiple gunshot wounds. Heck, why not just a nice quick shot to the head?

Is there an inconsistency here? We want to kill criminals, but we are squeamish about the manner of killing. Why is that? I think, if you can't face up to what you are doing and do it in the most efficient way, then maybe you shouldn't be doing it.

Just my random thoughts, not well researched at this point.