For me the most troubling part is how often a jury gets the wrong verdict and convicts people who are not guilty. For that reason alone, I do not believe we should have capital punishment.
Paradoxically, I do think some crimes should be punished by executing the offender's entire family. I think that would have a deterrent effect that mere execution does not. I also think it should apply to the highest levels of white collar crime. The Enron guys, for example.