Argument 1: Its immoral. You site God as the one that delivers justice, and God only who can decide whether or not a person can die. However if you believe the Bible/Torah are books of record as well as Scripture the argument doesn't hold up as people in Biblical times had many offenses for which the punishment was death. The idea thou shalt not kill is commonly taken as thou shalt not murder. Death was a punishment for crimes even under Moses himself. As far as cruel and unusuall punishment goes, the death penalty has been around for murderers heretics, etc. for thousands of years thus negating the unusual part of that statement. With regards to cruel, people who kill in our society cease to be a part of societal norms, cease to even act or think like a normally reasoning person. As such they revert to an animal state of mind where they reason like say a wolverine, which kills for no reason, seemingly for the fun of it. At the point where a human loses their human nature, and reverts to an animal state, the only similarity between them and a normal human being who has morals, and values, is the commonality of their bodies. Thus when a death penalty is imposed on this animal like creature, it is like putting down a man-eating tiger, or bear, or other animal.
Argument 2: Its a divisive Construct/Controversial. This is only a controversial matter if you look at it through the question: "Is it moral to take a persons life even if they have taken others' lives?" If you look at it through the frame work I set up in My first point, the real question is: "Is it moral to allow an animal like creature to have the opportunity to continue taking human life?" Just because you look like a human does not mean you act or reason like one. Its like redhouse said, why should we as moral human beings allow this "monster" to exist? Furthermore let us consider another idea, the idea that a country or society has the right to defend its citizens. For example, if another country were to come into our own and begin killing our citizens, it would be considered an act of war and we would act accordingly to begin defending our citizens resulting in the death of the invaders. If you look at the issue throught this paricular lens, it makes sense to prosecute to the best of our ability in defense of our society, and our citizens.
Argument 3: Its financially irresponsible. While it is true the some of the cost will be negated by abolishing the death penalty, a lot of that number is by definition untrue. Even people with life sentences have the opportunity to appeal, and you forgot to mention the financial burden of added inmates. Furthermore if you take into account the fact that over time Federal prisons could get crowded, and you will either have build more prisons or transfer inmates to state prisons, both of which cost money.
So what is the alternative?
I would suggest the alternative is to keep the death penalty around, but make it harder to use it as a punishment. In this way it is harder to possibly take an innocent life, but there is still a way to convict those found guilty of murder to suffer their due consequence of action. An action that is essentially an act of war.