The same logic applies to life in prison without parole, or even 1 year in prison. What business of the state is it to imprison someone who is potentially innocent?
Sorry, I don't buy it. Yes, the state makes mistakes, due to lying witnesses or misguided prosecutors. There are evils in our society, but that doesn't mean that we should ignore justice, or sacrifice justice because someone may, MAY die due to the wrongful acts of another.
I oppose the death penalty too, and I have a recipe for avoiding it: don't commit pre-meditated murder, and you are certain to avoid it.
Let's start with the obvious - one is reversible, one isn't.