Several reasons it should be halted:
Cost--numerous studies have shown the immense cost of the death penalty as compared to its alternatives. This takes away money from much-needed social programs and creates an inability for poor areas to seek it, creating an "arbitrary version of justice by geography," as the Seattle Times put it.
Innocence--Many innocent people have been exonerated on death row or executed and later found to be innocent. The inaccuracy is astounding and the cost--an innocent human life--is far too high.
Damage to prison workers--many prison workers have suffered PTSD-like stress after witnessing or participating in an execution. Some have committed suicide or started taking drugs or alcohol to cope with the psychological damage done to them.