I hope you don't mind if I answer your questions with questions of my own.
Who should decide which traits make a person a burden to society? What are the traits that would deem a person "expendable'?
I think of the profoundly mentally retarded, for instance, of the chronically ill. Should they be put to death because they put nothing productive forth?
Andrea Yates has a degree in nursing. She cared for her father on a daily basis, who died with Alzheimers. Is there not some way that her nursing skills could be productive in a psychiatric prison setting?