With the first one,you're going to want to use Ethos,or the appeal to emotions,for this to work. I would say this: There is an extent to which someone can be punished. If somebody committed murder,the death penalty,or more politely called "Capital Punishment",would honestly have no effect on them. It does not truly give them a chance to dwell on their actions and how they messed up someone's life. Not only that,but you also become a murderer if an innocent man is found guilty of a murder he didn't commit,which makes you no better than a murderer. Worse in fact because at least the person who actually did kill someone did it them selves and not with an executioner. I don't support Capital punishment because that puts someone else's blood on my hands.
As for the second one...I'd say this: By nature,humans are social creatures. We desire human contact and interaction. In fact,we NEED it in order to function normally. Capital Punishment only supports the tradition of "An Eye For An Eye And A Tooth For A Tooth." If you really want to punish someone,don't kill them physically,but instead mentally and socially. If you take away someone's ability to interact with people,it causes them to think back on their mistakes and it leaves them with no other choice but to confront their bad choices. Capital Punishment gets it over with quickly with no time to repent or ask for forgiveness,but life in prison with no chance of parole unless proven mentally capable by a team of psychologists,is by far the worst punishment you could ever give someone.