So you ask, how can one be opposed to abortion yet in favor of the death penalty? I frankly see no rational comparison between killing an innocent unborn child to executing a violent killer. One was denied their right to Life, Liberty, and the Pursuit of Happiness; the other took that right from someone else. Just like Jefferson said, Freedom gives you the right to do what you want, until it interferes with someone else's freedom, at that point the law must step in.
The question that really needs to be asked, is how someone can call for a killer's life to be spared yet sanction the killing of an unborn child? That just does not make any sense to me.
The likelihood of killing an innocent man has been significantly reduced thanks to recent developments in forensic science. There at least eight appeals in every state. Some states have as many as a dozen opportunities for appeal. Governors can grant clemency as well if they feel there may be a miscarriage of justice. I believe the Death Penalty is an essential tool for rendering the ultimate punishment to the most heinous criminals.