If I wanted to argue against death penalty, I'd definitely be using the arguments of set 1. Effectiveness of death penalty as a crime deterrent is a matter of several contextual and environmental factors and no one can say for sure that it is an ineffective policy. One could argue that it can at least reduce "planned" crimes. Uncertainty about its justness on the other hand is a very good argument against death penalty because even one example of its incapability of enforcing justice would suffice to question it. Only a few months ago a guy who'd been imprisoned for 10 years and was going to be executed was proven to be innocent after some other guy admitted to the crime. It's unbelievably scary how flawed our human judgment can be, even if made by the most qualified judges and based on the most overwhelming evidences.
