Why have something that doesn't serve justice?
Just think about this for a second, how would you feel if you were the innocent person who may be executed for a crime you didn't even do?
Also some sentences are handed down in an unfair manner. Some people may be executed based on circumstantial evidence or because of their past. For instance, in 1989 Carlos De Luna was released from jail, was found near the crime scene, and violated parole by drinking in public. He did not even have a drop of blood on him when he was found and the crime had just happened. Another convicted criminal who was romantically linked to the victim actually committed the crime but De Luna was still executed for the crime. This isn't the only case that this has happened in, there are many other innocent people executed.
How can you be sure if that was real evidence? Really think about this matter. Others have been found guilty based on circumstantial evidence because they had poor or unfair defense. What about the possibilities of someone planting evidence to make someone look guilty who is truly innocent. Just imagine if it were you.