I have several personal problems with the death penalty. Although I have every sympathy for the victims, I do not believe that legalised murder is the solution.
Firstly, can we ever be sure that a person charged for a crime is actually guilty of that crime? Sure, he or she may confess, but many people confess to crimes just to be the centre of attention, or for some other reason. Also, what about the evidence used against the criminal? Perhaps the evidence is analysed in the wrong manner, or is even falsified. I recommend reading John Grisham's "The Innocent Man." The main character (it is a true story) was in prison for twenty years for a crime he did not commit, and was later exonerated. There was fabricated evidence used against him, testimonies vouching for the man were ignored, and fabricated testimonies were used against him. He was supposed to get the death sentence, and it was only through the work of anti-death campaigners that he was freed.
Secondly, if a child molester, rapist, or murderer was sentenced to jail indefinitely, as compared to legalised murder, what is the difference to society? That person is not really going anywhere, are they? The only difference I see is that they are stuck inside a small cell for the rest of their lives, insted of receiving a lethal injection,
Lastly, my question about what would you do should we be able to completely rehabilitate a criminal. It was to see if any pro-death person could see another way that they could have legal closure besides the death penalty sentence. It is not a reality yet, though. I am glad at least one person tried to think about what I wrote. As for moral objections, changing the way people think and act would obviously draw objections, even if they are murderers or rapists or whatever else deserves the death penalty.