Actually I don't think so. I don't remember where I read it, but with all the appeals and other automatic hearings involved in executions, that killing them is more expensive then letting them rot in prison. I used to date a girl who went to Sam Houston State in Huntsville. She was a member of Amnesty International and used to go protest killings at the prison there. She was also a vegan. Imagine her discontent when I used to bring double-meat hamburgers into her apartment. Good times, very nice girl. She joined the Peace Corp after college and married a French-Canadian named Bruno. The last time I talked to her I couldn't stop laughing that she was marrying a guy named Bruno.
Personally, I don't think of whether or not to take a life based on potential economic benefits. If I think the death penalty appropriate, even if it costs more, it doesn't affect my opinion. However, the fact that more and more innocents are being found on death row bothers me too much to whole-heartedly support the death penalty. One can point to the appeals process and say it works (since it does, apparently, end up reducing a significant percentage of death penalty convictions either to lesser punishments or exoneration), but I fear the ones that may slip through. I think of Todd Willingham. The science of the time said the fire that killed his kids was arson. The science of today says it wasn't. A man convicted of arson in a nearly-identical fire was set free recently because of advances in the field of arson detection. Willingham remains dead. Even with the new advances in arson detection, one of the jurors in the Willingham case said she would still vote to convict because Willingham "didn't try hard enough to save his kids" (which, by the way, says to me that a whole bunch more people need to be put on trial and sentenced to death. All those neighbors who testified that Willingham didn't do enough to save his kids were standing there doing even less. According to that juror's thought process, they committed capital murder, as well). There are so many cases that are so heinous that my immediate gut reaction is that the only appropirate punishment is death. But from my readings, there are too many cases that result in the death penalty that rely on evidence that isn't nearly as cut-and-dried. Until we have a system in which we can guarantee that only the absolutely, positively guilty people get the death penalty, I'm not going to be a fan. But that's just what I think.
The death penalty, unfortunately, is probably a pretty good hedge against pitchfork, lynchmob justice. Not to stereotype, but I think there are some states where, if there wasn't a death penalty process, people would probably just take justice into their own hands, and they would do so with far less consideration for facts, evidence, or the age, mental capacity or possible pain & suffering of the "convicted." And it wouldn't be restricted to murderers, either.
But then when those vigilantes kill, the mob can go and murder the vigilante, too. Eventually all the hotheads who can't function in society will be dead and we'll get on with life. If someone is willing to kill because of a perceived injustice, then something was going to get to them eventually and set them on a killing spree. Who's going to riot when it's proven beyond a shadow of a doubt that an innocent person was put to death. Is the prosecutor fair game? The jury? The judge? I mean, not only are those who worked to put an innocent man to death not going to be put to death themselves, it's unlikely they'll receive any punishment at all. That sounds like a cause I could riot behind myself. I just don't believe we're all hanging on by a thread like that. I mean, are we all really so different among the various states? Are Texans always on the verge of a riot and vigilante justice while those in Michigan can get along just fine without it? Where were the riots in the 1970s when the death penalty was briefly illegal? Was there a big uptick in vigilante crime during this time because the death penalty was taken away by the Supreme Court? And in states where the death penalty is rarely enforced, does simply having it calm nerves? I mean, if we had a death penalty but made it so virtually no one qualified, would that avoid all the riots that will bring down the government or whatever?