1.
Executions cost more than life in prison.
$2 million per person vs. $500,000 (4x as much!). Free counsel for defense, for appeals, maximum security on a separate death row wing.
2.
The innocent may be wrongly executed.
Since the DP was reinstated in 1976, 82 inmates have been freed from Death Row. That's 1 Death Row inmate found to be wrongfully convicted for every 7 executed.
3.
Is not a deterrent; crime rates have not gone down.
In fact, the murder rate in the US is 6 times that of Britain and 5 times that of Australia. Neither country has the DP. Texas has twice the murder rate of Wisconsin, a state that doesn't have the DP. Texas and Oklahoma have historically executed the most number of DR inmates, yet in 2003 their state murder rates increased, and both have murder rates higher than the national average.
4.
Life in prison also guarantees no future crimes.
5.
Some religions forbid death penalty: Catholic, Presbyterian, Quaker, Amish, Mennonite.
6.
Killing is wrong.
7.
Many Death Row inmates were convicted while being defended by court-appointed lawyers who are often the worst-paid and most-inexperienced and least-skillful lawyers.
The American Bar Association published guidelines for a good defense in a death penalty case: (a) attorneys with prior experience working a capital case, (b) 2 attorneys, 1 investigator, 1 mitigation specialist, and (c) fully funded to pay for travel, private eyes, evidence testing and other things needed to investigate the case. Yet no state meets these standards. And few states pay their state-appointed lawyers well enough to retain competent, effective lawyers.
8.
Violates international human rights laws.
9.
No longer practiced in most sophisticated societies.
10.
Promotes killing as an OK solution to a difficult problem.
11.
Death sentences are handed down arbitrarily, not in a fair manner.