A killing is still a killing...
This is a fact, and I agree with that.
...and makes whoever does it a moster even if it's by proxy.
This is opinion. I think that one SHOULD, in fact kill any person that comes into a country with deadly intent, or substantial reason to believe they have deadly intent. Plus, as a "capitalist", I prefer that my tax money doesn't go to provide these scumbags with comfortable jail cells, so I advocate getting rid of them to not waste tax money.
I agree with Tal on this point (big surprise).
Let's assess the logic of prisons:
Okay, you murdered somebody in cold blood. Are we going to sentence you to a lifetime of hard labor? Nooo, you could escape. We'll lock you in your very own private room where you'll get any magazine or book you want (provided it has no sexual or violent content) and you'll get free meals and a bed and a warm place to sleep. You won't even have to work for it. You'll never have to make a big decision again. Just be sure to send a nice letter to the family(ies) of the victim(s) who are currently paying for your jail cell.
I don't know about you, but to me, this doesn't make much sense. The way I figure it, you either sentence them to hard labor (farming for the financially disadvantaged or for their own food, making license plates, manufacturing simple tools, you know the drill), so they're working for their living and paying their debt to society, or you execute them. I feel the former is better in almost all of the cases. It creates in a prisoner a sense of responsibility and purpose, which is key to rehabilitation and also helps them pay their debt.
However, there are a few cases in which placing a prisoner in a somewhat secured workplace is not secure enough, and it is not feasible to make it so. There are also cases in which the crime is so heinous, an extreme deterrent is needed for prevention. In these cases, I would strongly encourage the use of the death penalty. I would elaborate on more specific conditions on persons who should get the death penalty and how a death sentence should be carried out, but this post is too long as it is.