A brilliant argument. Your superior wit and intellect is obvious; please don't abuse me with it - I can't take much more!
Your idea that the death penalty is wrong because sometimes people get offed who are innocent really is quite lame.
You could use the same argument for any kind of punishment.
Dying in prison of natural causes is just as bad as languishing in jail for 10 years and then getting a little shot.
But thus do I councel you, my friends: distrust all in whom the impuls to punish is powerful!
They are people of bad race and lineage; out of their countenances peer the hangman and the sleuth-hound.
Distrust all those who talk much about their justice! Verily, in their souls not only honey is lacking.
And when they call themselves "the good and just," forget not, that for them to be Pharisees, nothing is lacking but power!
(Nietzsche, Thus Spake Zarathustra, Tarantulas)