you're making a point against the infallibility of the prosecution process here, but in any case not against the legitimacy of the death sentence itself.
I understand the distinction between the legitimacy of the death penalty and the way this sentence is used in a particular set of rules.
But when it comes to decide if the death penalty is a punishment which can be applicated in this particular set of rules, you have to deal with a moral dilemma. Since you know that applying the death penalty will result in irreperable mistakes (which is not the case for other kinds of punishment), you have to decide which moral principle is more important:
1. according to proportionnality, one who killed shall be killed
2. a decision of justice cannot result into killing an innocent
then you can choose than the legitimacy of the death penalty is more important. IMHO, it needs more than proportionnality to be justified.
It's this reasoning which leads to the moratorium.
But it's not the reasoning of the death penalty opponents. You're right, Mr.Bennett, in principle every death sentence is a convincing case against the death penalty, otherwise any exceptions void the principle. That's what I intended to say when I wrote that focusing on cases doesn't mean they support death penalty for other criminals. Either MM. Mumia, McVeigh or Dutroux.