Mentally retarded people are closer to being childlike in their capacity to learn and understand than they are to being adults, even after reaching chronological adulthood. The definition of an adult being a person who not only can determine right from wrong, but who has the knowledge and understanding and mental ability to make independent decisions in living. We are humans. Let us show our humanity by not executing mentally retarded adults who commit crimes. The population can be protected, and justice can be served by removing the mentally retarded adult criminal to a location away from society.
Incarceration protects society.
Killing prisoners takes away time from their further growth in consciousness. From a spiritual point of view we are all here to grow in consciousness. Part of this growth is learning that as humans we show humanity by acting for the higher good of each situation, which means harming no one, including ourselves, including incarcerated criminals. We are each part of the web of creation. Even the most hardened criminal, through time, can come to realize the underlying spiritual harmony supporting all.