I don't know why it has to do anything with "left wingers". It's the "right wing" states that usually have the death penalty, and why it's so expensive, they're the ones that should explain themselves.
Anyways, look at Florida. They send the most inmates to death row, but also have the highest number of death row inmates who were later exonerated, acquitted, or had their charges dropped. That's one good reason to get rid of the death penalty. Our Justice System evolves as technology advances, where there's more evidence to correctly convict someone, it gives the judge and jury more insight in making a better decision.
Our legal system is setup by our government, led by greedy politicians, in a Capitalistic society. The only reason I think it would cost so much.
I normally tend to avoid these political discussions, but I just have to comment on these points.
First, you're claiming that the "right wing" is responsible for making it more expensive simply because it is "right wing" states with the death penalty is woefully naive. To explain I'm going to bring up something even more controversial than this topic. Please understand that this is not to cause the topic to digress, but only because it is a good comparison. Look at what is happening with abortion in, what you would likely call, "right wing" states. New laws and regulations are being put in place by the "right wingers" to deter the use of abortion, because they oppose it but cannot stop it. Impairing it is the best they can achieve. If "left wingers" cannot stop the death penalty then they too will attempt to impair it by instituting new laws and regulations to deter it, which increase costs.
You see, my point is that thanks to the system of government we have, even if the majority viewpoint is one thing, the implementation can be greatly effected by the minority viewpoints.
Your reasoning for getting rid of the death penalty because mistakes can occur in the judicial system is also faulty because truly that thinking implies, with as much strength, to the suggestion that the judicial system itself should be gotten rid of because of the mistakes it has made. That is utterly ridiculous.
That reasoning would be better put to use arguing for automatic appeals for any death sentence and a strengthening of the appeal process, to diminish the likelihood of a mistake. This is also an argument just about anyone will agree with, by the way.
Costs are high because the money has to be spent for one thing or another, such as the appeals process. Also, keeping the prisoners throughout the process and, I believe many of them are kept in solitary, which is more expensive than keeping them in the general population, add to the costs.
By the way, I do not support the death penalty. I just think your arguments are crap, which is why I'm commenting on them.