All good points you make regarding the death penalty and they pretty much sum up why I've never supported it. I think the biggest thing for me is the chance of an innocent person being put to death, especially when you here of cases where people are exonerated after being on death row (or worse, found to be innocent after being executed). I agree with you in saying I don't think I'd like to live in a society where that could happen.
It's cases like Jill's that start to confuse my thoughts on the death penalty. I think it might've hit home because I can relate to their circumstances (a couple of years younger, engaged, etc), but I just can't get past how awful the husband would be feeling right now. If that happened to me, I don't know that I would ever get over it.
I think you can only discuss the death penalty in cases that you have no connection too. I think if this happened to a family member or someone close to you, it would be much more difficult to argue against the death penalty. So from a neutral position, I agree with everything you said and oppose it too. If it happened to someone close to me however, I'd want to pull the trigger myself.