I usedb to be against the death penalty because it is irreversable until someone presented me with the following counter argument: Innocent soldiers die for the good of the country when they give their lives. Everybody appears to accept that dying for the good of the county is admirable.
If a wrongfully convicted person dies it is also for the good of the country. It still serves as a deterrent and helps prevent future crimes.
It is not much different from a drafted soldier dying.
The true guilty being executed is no problem. They made their choice when deciding to commit the crime.