"My gut reaction is "kill 'em". But my considered reaction is "what if we're wrong"." - 1Poorguy

That is because you are intelligent and thinking enough to recognize that there is often nuance in the world and that you (and the world in general) can often be wrong.

I absolutely guarantee that people who are pro death penalty don't actually think about it. To them it is a black and white issue. The people on death row were convicted of a horrible crime so they are terrible people deserving of death. Simple. Binary. Black and white. It doesn't even occur to them that the justice system is far from perfect and innocent people can get caught up in it. Anyone who takes a second, looks at the data and sees that the justice system is often imperfect and regularly biased against people who are easier to falsely convict of death penalty crimes (poor, mentally ill, uneducated, often minorities) would be against the death penalty. How could they not?