When someone cause harm to us, we generally look for revenge because of an instinct which adds a new ring to the chain of violence. In a modern society, we must respond in a better manner and we should demonstrate a full respect for life even if the person is a murderer. In a system with the death penalty, vengeance is encouraged which causes another killing. For example in the United States, victims' families are allowed to watch the execution of the murderer whom they have not forgiven through the trial, but most of them cannot stand witnessing it. When it is asked whether they are satisfied or not by the death, they usually say that ending a life is so cruel and inhumane that they feel pity for the deceased murderer. They realize that their agony does not need retribution to heal and responding violence with violence breeds more violence.
In addition, the judging system may not be reliable which can cause a fatal error. When the suspect is executed it is not possible to make an excuse. We can see many mistakes have been made in sentencing people to death. According to the Human Rights Organization report in the United States, more than 70 people have been released from death row after evidence of their innocence have emerged since 1981. During the same period of time, over 500 people have been executed. These statistics represent that innocent people are executed and there is an absolute risk of executing more. Judges or Grand Juries believe false witnesses or examine the crime evidence in a wrong way. Therefore, advancements in science and DNA testing has changed the destiny of the innocent suspects dramatically. DNA testing became available in 1995, due to advances in science. By the aids of the new techniques, policemen and judges reinvestigated the evidences and found some suspects not guilty or changed the death penalties to a sentence of life without parole.
On the other hand, it is argued by some people that death penalty is the ultimate warning which deters crimes and preserves moral order.