[See, e.g., source; source]

The problem with the former is that there will of course will be the unrepentant, and the latter rarely happens "swiftly" and  the cases of wrongful convictions. 

As for the death penalty being a deterrent? According to the Death Penalty Information Center death penalty states average 4.7 murders per 100,000 residents while non-death penalty states average 3.8.

I did take some consolation when the topic came up again my senior year, and I was no longer alone in being opposed to it. 

My reasoning for opposing it has evolved as I’ve aged. I believe human life is so precious and miraculous that it must be protected at all costs. I believe nobody should have the right to kill another human being, even if that person did the unthinkable. Either all human life is precious, or none of it is. The only caveat I’ll make is that if your life is in imminent danger, it’s understandable that you do whatever you must in order to protect yourself, even if that means killing your aggressor. 

But I also don’t believe in the punishment model as a form of consequence. I believe the main goal of our prison system should be rehabilitation with as minimal recidivism as possible. Some people are too broken, too far gone, to ever walk freely amongst us again. But they didn’t choose the circumstances that scarred them so badly. Locking those people up is as much about protecting society from their erratic actions as it is about protecting them from themselves.