I can see that this has become quite the heated debate.
El Cid makes a good point that he kinda has been backed into a corner here judging by the pro-death penalty and anti-death penalty ratio in this forum.
But there might be a good reason why he's in minority.
In the western world, the death penalty has almost been completely abolished. As you can see by this map, The States are among the last few countries in the Atlantic region to maintain this practice.
Hint: Blue is complete abolishment. Brown is full practice. Orange and green are somewhere in between.
It's easy to notice that most of the countries with good internet connectivity and a high ratio of English speaking people are blue in color. On top of that there are heavy protests against capital punishment in the states themselves. Most executions have to deal with crowds of people lining up around the prison, protesting the deed. With this in mind it's easy to see why few people in this discussion thread are willing to stand up and defend this form of punishment.
Now, if I allow myself to wander of topic, I wish to attempt to understand the general American mentality. I seem to be getting the impression that they're kinda stuck in their ways. Hesitant of changing things, possibly out of fear that it might screw with the status quo and make things worse.
I started thinking about this as I paid attention to the recent health care reform protests. Despite being the only western country left that doesn't offer a universal health care there sure is allot of resistance for it. People scream bloody murder, claiming that this is the start of a fascist regime. Now if that were the case, I wonder why the rest of the western world doesn't seem to see it in the same way. In fact, the general attitude that other westernized countries have towards the American health care system feels borderline sympathetic.
Then we have these examples. America still uses the Imperial system as opposed to the Metric system. A measurement system that many consider to be considerably easier and more efficient to use. Unusually loud protests are heard over there about the Evolutionary theory being taught in schools, instead of the biblical creation myth.
Now, I'm not attempting to take pot shots at this country. While many "enlightened" people would look at this list and think "Gee. America sure sounds dumb." consider this: This is the country that managed to become the leading figure of the world during the late 20th century. The economy of the world revolves around America. They're responsible for many of the greatest technological innovations in these recent times. They put man on the moon. These are not dumb people.
But despite this, they seem to cling onto the older traditions. The practice of Capital Punishment are among those traditions. Whether or not the "old" is better then the "new" or not doesn't even seem to become a discussion among many people living there. I've entered countless of conversations where I'm attempting to describe "my way" as opposed to "their way" and the results of those discussions seem to often fall under these two categories: 1) They've never attempted to research "my way" and are perfectly contempt with "their way" and have no desire to hear about any alternatives. 2) They've researched/studied/know of "my way" and often agree with me that it's better but usually don't see the point in switching.
They're not the only ones to fall into this "stuck in their ways" pitfall though. After the fall of the Roman Empire, the European nations were incredibly resistant towards adopting the Arabic number system instead of the Roman one. While the old system certainly worked, the new number system from the east proved to be much easier to use. Especially when dealing with high numbers and complex calculations. It wasn't until several centuries later, during the invention of the printing press, that the Arabic numbers became commonly used among the Europeans.
So what's my point? Good question. I don't fully know myself. These half baked thoughts of mine are still a work in progress. I believe the death penalty is a barbaric form of punishment and I have a hard time understanding why anyone would support it. Maybe this rant of mine is my way of attempting to find a way to explain it to myself.