"I wonder if he doesn't give up too quickly on looking for a reasoned basis for being opposed to the death penalty. For example, couldn't he argue that the death penalty brings with it a virtual certainty of mistakes and therefore the killing of innocent people; and that the deliberate killing of innocent people is nearly always wrong even if it can be shown to have good (utilitarian) consequences?"Yes, he's right. I could - and I actually do. If pressed for a reason why I oppose the death penalty, the certainty of making mistakes is the one I usually give; I'd forgotten to mention this is the post. I wonder about my own consistency here, though. While someone executed by mistake is an innocent who has been deliberately killed, when we talk about deliberately killing the innocent, we usually mean they have been killed with the knowledge that they are innocent. Without this, it's a much weaker reason. You could say that war brings with it the certainty of 'deliberately killing the innocent' in Norm's sense too - so if this reason is to rule out the use of the death penalty, it should also rule out war, surely? But neither Norm nor myself are pacifists.
The other point that occurred to me has to do with the general idea of values and prejudices. I'd agree that we shouldn't give up on finding reasons for the positions we take. I should've qualified what I said by adding that I think a lot of the positions we take are sort of post de facto rationalizations of prejudices we already have. This means that they aren't pure prejudices - and we could say that the positions we change in the face of evidence are relatively free from prejudice? - but I still think that prejudice forms a large part of the positions we take, even though we insist they are rational. I wouldn't say I'm comfortable with this, really. I don't know quite what to make of it - but I do think it's true.