The thing is, as long as humans are the ones who are served with the task of delivering justice, there is always room for error, there's always room for biases and personal beliefs getting in the way. Not even the most stoic person can feel no emotion when presented with the sort of gruesome cases described above. That's why we have juries, to hopefully come to an impartial conclusion, but even so, any decision that is made is going to be somewhat slanted by the emotions of those involved.
Am I in favor of the death penalty? Yes and no. When I was younger, I was all for it, but as I've thought about it more, I see the problems with it. Namely, the executioner, which I'm sure has some sort of long-winded, unnecessary, politically correct name nowadays, is also human, and also probably has a lot of feelings as he's administering the injection. It could well be, "die, bastard!" that he's thinking, but what about after the adrenaline wears off and he has to look at himself in the mirror the next day? If you kill another human being, there are going to be effects from that, unless you're an actual psychopath.
This brings me to why I do still somewhat agree with the death penalty remaining in existance. A true psychopath is never going to be able to reintegrate into society. One would hope that such a person would be locked up for life after committing crimes like serial murder or pedophilia, but one thing psychopaths are also good at is being charming. They may excel at good behavior just so they can get parole, and end up reoffending. Or they could escape from prison. Or, they could just carry out their sadistic urges against other inmates. There's a reason prison rape is such a common trope, after all. If someone feels no remorse, and is just a drain on tax dollars, then it seems pointless to keep them alive.
Speaking of tax dollars, prisons are a far cry from the way they used to be when inmates had to do hard labor and subsist on bread and water. I'm not saying they're pleasant places to be, but they have TV's, exercise equipment, libraries, visits with loved ones, access to free therapy/medication, etc. Is that right? Should the worst of the worst be able to take advantage of such pleasantries? I think not. Taking advantage of people is often what a psychopath does best, do we really want to put them in their element?
There's also the fact that, although this usually applies to those who commit petty crimes, some people actually do things to end up in prison on purpose so that they don't have to live on the street, or some other unbearable situation. Prison is actually better and safer in such circumstances, and there's definitely something wrong with that picture. As I said, murder is usually either a crime of passion or an expression of power and control, and rape is always about power and control, so this doesn't necessarily apply. Sling Blade is about the best example I can come up with as a depiction of an actual murderer who couldn't cope with life on the outside, so he killed someone else to get back to the only life he'd basically ever known, but, epic movie though it is, it is fictional. Plus, that guy was in a mental hospital, not a prison, so I wonder how the dynamic would have been changed if he had been in prison instead.
With all that said, I can't come to a definitive answer. I definitely think that taking out the garbage, so to speak, is a base human response to unspeakable horror, and no one should be shamed for it. I also think our prison system right now is broken, although that's certainly not a revelation, people have been saying that for years. But what does it accomplish, honestly? yeah, it probably gives the families of the victims closure, and it's liberating to clean up some of the scum of the earth, but at the same time, it hasn't been that much of a deterrent. It's too large and complex an issue for me to really make any solid conclusions about.
The glass is neither half empty nor half full. It's just holding half the amount it can potentially hold.