I oppose the death penalty for a variety of reasons.
For one - it is not a deterrant. In most cases the death penalty is not a deterrent in that most murders involve spur-of-the-moment passion. I honestly don't think most murderers think about the death penalty before they pull the trigger.
I tend to agree with Clarence Darrow (in the Leopold-Loeb Murder Trial of the late 1920's): "
...it's better to lock the murderer up for life and study him in the hope of understanding ,and thereby preventing, some future murder."
In addition, states without the death penalty have much lower murder rates. The South accounts for 80% of US executions and has the highest regional murder rate.
This leads me to think that the death penalty has little effect on murder rates and more likely something else is driving that.
The other reason I totally disagree with the death penalty is that it is inequitable. If the death penalty were fairly applied across race and class and crime I might in theory support it. But the reality of it is that isn't and probably never will be.
Race, sex and ethnicity is a factor - whether it is the race of the victim, or the race or sex of the perpretrator. Statistics show that a black person is much more likely to have his case remanded to the death penalty phaze then a white person and a black person committing a crime on a white person is much more likely then a black on black crime. Likewise men are many more times likely to face the death penalty then women.
http://www.deathpenaltyinfo.org/article.php?scid=5&did=184
Class plays a role in who gets the death penalty and who gets life. Poor people are much more likely to recieve the death penalty for the same crime as rich people.
Lastly - the question of executing an innocent person. More and more death row cases are being challanged with new evidence and exonerated. Of course, once their dead there is no longer much push to prove innocence so we have no idea how many innocent people might have been executed. Dead is dead. As long as there is any question whatsoever of innocence, I can not support the death penalty.
Frankly, why not life in prison - no parole - in reality, not theory?