All praise be to Allah, peace and blessings be upon Prophet Mohammad and upon all of his family and companions.
Penalties have been stipulated in Islamic Law to maintain its objectives i.e. what the scholars called “The Five Necessities” which are: religion, life, regeneration, money and brain.
Moreover, it`s been discovered that all of them were protected in all earlier Laws. One of these penalties is Al-Qas`sas (Law of Equality) which has been stipulated for a few crimes; whereas, other Laws have stipulated the death penalty for over two hundred crimes. This penalty was originally stipulated in Islamic Law to maintain security of the Islamic society since a rotten apple may damage the good ones , thus it must be taken out. Allah, The Almighty, says in this regard: “In the Law of Equality there is (saving of) Life to you, o ye men of understanding; that ye may restrain yourselves.” {Al-Baqarah/179}.
The Islamic Law has made it an obligation to execute Qas`sas on the one who commits murder deliberately, and this sentence is what serves justice right. Allah, The Almighty, Said (What means): “The recompense for an injury is an injury equal thereto (in degree).” {Ash-shura/40}. He Also Said: “The prohibited month for the prohibited month,- and so for all things prohibited,- there is the law of equality. If then any one transgresses the prohibition against you, Transgress ye likewise against him. But fear God, and know that God is with those who restrain themselves.” {Al-Baqarah/194}.
However, the Islamic Law has left the door open for dropping this penalty, and so the guardians of the murdered enjoy the right of doing so in return for taking the Diyyah (blood money) from the guardians of the murderer , or in return for nothing. Not only that, but the Muslim scholars had decided that if a member of the victim`s family remitted the murderer, then the death penalty is nullified. Prophet Mohammad (PBUH) said (What means): “If somebody is killed, his closest relative has the right to choose one of two things: either the Blood money or retaliation by having the killer killed." {Al-Tirmizi }.
Moreover, Islamic Law has encouraged making remission as Said by Allah, The Almighty (What means): “But if any remission is made by the brother of the slain, then grant any reasonable demand, and compensate him with handsome gratitude, this is a concession and a Mercy from your Lord. After this whoever exceeds the limits shall be in grave penalty.” {Al-Baqarah/178}. This way, Islamic Law has reduced the death penalty to the lowest degree possible: Paying the Diyyah.
As for abolishing this sentence altogether, it is tantamount to being merciful to the murderer and cruel to society; particularly, the family of the victim. Such a thing will lead people to seek retaliation without paying attention to the effective laws of the general authorities, and this will definitely lead to corruption and undermine security. And Allah knows best.