The death penalty costs too much, takes too long, invites abuses and doesn’t work. The possibility of being executed has not been a deterrent for criminals who commit capital crimes. Their trials take longer, and appeals can add many years from conviction to punishment causing justice to be delayed and thereby denied. If the victim is high profile, the prosecution and defense are tempted to pander to public opinion. If the accused is indigent, lawyers are tempted to raid the defense fund as they did for the Brian Nichols trial, taking $2.9 million, which left no money to defend other indigents. Witnesses of questionable integrity are tempted to offer false testimony in exchange for lenient treatment in their cases.
God said, "Vengeance is mine" not because he is vengeful, but because vengeance tempts humans to behave as they shouldn’t. God doesn’t make mistakes, but humans do, and those mistakes cannot be corrected after an innocent person is executed. There are better solutions such as life without parole, and while life exists so does the possibility of finding God. Charles "Tex" Watson committed horrible murders in 1969 and is incarcerated for life, but after finding God in prison, he has helped other inmates do the same.