Firstly, prison populations are spinning out of control. Several studies (http://online.Ccj.Pdx.Edu/resources/news-article/prison-overcrowding-is-a-growing-concern-in-the-u-s/) have proved the negative effects of overcrowding on prisoners. Thus, the extra evil ones should be killed, firstly, for the psychological well-being of lesser offenders, and secondly to prevent overcrowding.
Also, the only foolproof way to ensure no more recidivism is to actually kill the worst offenders. Even in max security prisons, the sheer fact someone is alive heightens the chance of them harming or killing other people.
How many innocent people have been killed by evil people that enjoyed killing and want to keep on killing? Some people cannot ever be reformed. They will kill again and again and again until they are stopped. The death penalty is the only way to assure the general public that these evil people will never kill another innocent person.
Is imprisonment for life a more efficient punishment for murder? If you were sent for a death sentence then you wouldn't suffer as long, because you get killed almost instantly. Imprisonment could cause you to suffer depression, insanity, or other mental breakdowns. It would cause much more pain over time then barely any at all.
It's ridiculous. What sort of precedent does it set when the state falls down to the same level of what the opposite motion refer to as 'evil' as the perpetrators themselves? An eye for an eye does indeed make us all blind, and under that guise alone capital punishment could well be considered immoral.
But more importantly, when we consider the implications of the death penalty in a purely rational manner, it is also flawed. In the United Kingdom, where I reside, numerous individuals have been found innocent of offences that would be deemed serious enough to warrant execution whilst the aforementioned people were imprisoned. So had we still had the death penalty, we would have killed those people, and in some cases, will have created new martyrs for a political or fundamentalist cause, potentially compromising our national security.
What sort of deterrent is Capital Punishment when most people committing such offences are so seldom motivated by a 'soft punishment'. Indeed - for terrorism or sexual offences it would be extremely difficult to see the concept of 'getting away with a slap on the wrist' as applicable to the causes of such crimes.
Let's focus on prevention and rehabilitation rather than detention and execution. We've moved on since then. I shall finish with the words that I began with. The death penalty is revenge. Revenge isn't justice.