YANBU.
In my (probably not very well informed) opinion, the death penalty is a direct result of politics bleeding into the judiciary and religion bleeding into politics. State attorneys are politicians. They need to be seen to be tough on crime. If their electoral base is formed of fundamentalists (anti abortion, supporting gun ownership, supporting execution), then they need to pander to the instincts of this group. To be re-elected, you can't be seen to be lenient on killers, and to appear competent, you can't be seen to admit that your office got it wrong in prosecuting its case in the first place. You'll fight tooth and nail to uphold an unsafe conviction, in the face of damning evidence to the contrary, just to save face.
The Guardian said this about Federal involvement:
"Al Sharpton, who attended the protests in Jackson, said he would be pressing for new legislation to ban death penalties in cases relying only on witness statements.
But it is unlikely that a new law overturning the practice could be passed in Washington. It is convention that individual states have control over death penalty rules, and the federal government can only lead by example in its own execution practices; it does not generally have the power to tell states like Georgia what to do"
Have no idea if that's an accurate summary of the situation, but it sounds pretty lame if it is. "Convention" sounds like cop out.
Whoever said those convicted of murder should be used as human guinea pigs must live in a very dark place. I would not want to be inside your head.
As for the child rapists etc. I imagine there's a good chance they were the abused once. Executing them once they have been damaged and gone on to do damage to others - does this prevent further child rapes etc? I seriously doubt it.