1) Life without the possibility of parole is less expensive by $millions.
2) California has executed at least 8 later Proven innocent.
3) State execution is killing with malice aforethought (definition of murder)
4) Failures in justice leave the criminal free, and the state guilty of the crime of murder in the name of the citizens.
5) The US government has failed to stop an execution when it knew of the innocence (FBI kept quiet).
6) Suffering is suffering, and is not lessened by vengeance, so "closure" is not the result, but a miscarriage of justice is cause for guilt for all.
7) For the religious, the Word is "Vengeance is mine, sayeth the Lord."
Capital punishment is a failed primitive measure that proves expensive and counter productive.