Is it inconsistent to be pro-life and pro-death penalty?

One of the oddest arguments I've heard against the pro-life position, I first heard from one of my history professors in college. He asked the class how many were pro-life regarding abortion. Then he asked how many of those were for the death penalty. Then he smirked, thinking somehow he had caught the pro-lifers in an inconsistency. Most of those who were pro-life also supported the death penalty, and my history professor thought that to be inconsistent.

He's not the only one either. At the time, I thought he was just a peculiar person that hadn't thought things through. Since then, I've heard this same argument come up several times from several different places.

Here's why I think it's so odd. There's a huge difference between killing a person who has committed no crimes, and killing a person who has committed murder. One is innocent, and the other is guilty. People are pro-life, because they think the unborn are innocent human beings, and it's wrong to take the life of an innocent human being. They are for the death penalty, because they think murderers deserve the death penalty. Where is the inconsistency?

If there is any inconsistency at all, it's in those who are pro-choice but also against the death penalty. How odd is it to suppose that it's perfectly alright to kill innocent people, but it's terribly wrong to kill guilty people? You might object by saying, "But pro-choice people don't believe the unborn are people." That's probably true in the majority of cases, but there are some who do. But my point isn't to argue that pro-choice people are inconsistent if they are against the death penalty. I'm just illustrating the absurdity of them claiming pro-life people are inconsistent if they are for the death penalty. If there is any inconsistency at all, it is on the part of pro-choice people who are against the death penalty.

Now I'll be honest with you. I'm pro-life, but I have some reservations about the death penalty. Mostly, my reservations come from my lack of confidence in the justice system, which has grown over the years. I would be all for the death penalty if guilt could be established with certainty--raising the bar quite a bit above "beyond a reasonable doubt."