I'm not a fan of the death penalty in the US as a method of deterrence, as most murders are crimes of passion and impulse... somebody didn't intend to kill anyone but they did. You can't deter somebody from an idea they haven't had yet until it suddenly happens and they can't take it back. The social contract and our natural inclination to try to get along with each other means that even if there were no death penalty, the vast majority of people would still somehow resist the urge to kill each other.
I'm also not a fan of the death penalty as a matter of "justice" because justice isn't really defined overall and I don't think it will be. We could talk about punishment equal to the crime, but our justice system itself doesn't even fully believe in that. Deals are cut all the time for sake of conviction rates, or getting the "worse" criminal in a group. You can steal $5 million from your neighbors and get 5 years in prison or rob a corner store and get 5 years in prison. And say murder is on the table... well if you kill one person you can say fine, death penalty. What if you kill 17 people? We can't kill you 17 times. Justice is so ill-defined and fluid a concept that I don't trust it to be used effectively by the state.
For that matter: there are people who wouldn't trust the state (remember, it's the state that executes) for pretty much anything else in life: licensing, taxes, requiring them to get car insurance... but when it's time to kill somebody suddenly they're all on board? Why does the taking of life not rise to the same level of scrutiny as what we demand when we want a pothole in the road fixed, when it's placed in the hands of the same monolithic unfeeling bureaucracy populated by the same fallible human beings?
I do not support the death penalty because there have been legitimately innocent people on death row and statistically there are more we will find out about. With that hanging over the question, I do not take the belief that someone who didn't commit a crime should "take one for the team" to keep the death penalty viable for the real criminals. That's flawed thinking that invalidates the deterrence theory. If you can be killed by the state even if you didn't do anything, then why not go ahead and commit crimes and at least get the momentary benefit of those crimes and just hope you don't get caught? And the executioners cannot be guaranteed in all instances that they are truly executing a guilty individual, so either you must hire sociopaths who cannot psychologically bring themselves to care about killing an innocent person, or you must deal with high turnover as executioners don't find the process fun and don't tend to volunteer for many of them.
Not only that, but saying that the potential number of innocent people is low seems incredibly insensitive to me since it's not just about the number of people killed. Murder of an innocent is punishable by death in the system. Who's willing to sign up for a job in which you get to kill people but yeah there's a possibility that we'll have to then kill you for killing people? The possibility might be 1% but that's both cruel to the executed and executioner. And somebody above who'll probably still watch this thread was mentioning things like banning cars or windows... that they equate accidental deaths with the willful authorization by the state to seek out and capture and murder people is itself unfortunate. Yes, every death of an innocent is unfortunate, but there has to be a higher standard for permitting the state to murder on society's behalf. Since that's what we're doing: unless we can perfectly determine guilt in all instances of the death penalty, we are saying that murder is illegal, except when the government does it. I would not call that justice, by any measure or definition.