In the name of Allāh,
the Beneficent, the Merciful.
Peace and Blessings of Allāh on Mohammad.
Allāh–the Glorious and the High,
Lord of the worlds
Mohammad–who brought the world
to our feet and eternity to our arms.
Some secular laws allow murderers to return to society where they may again commit murder and perhaps other crimes, and where in prison they may be supported by the families of their victims (through their taxes; and criminals are given such facilities as gym, computers, study material; etc, that some tax-payers and members of some victims may not be able to afford for themselves or families; and they are probably better fed than some of the taxpayers that shoulder their bills). Islam rids society of them permanently–(In the case of unintentional murder compensation may be effected–Qur’an 2:178; 4:92).
Allāh the Wise tells us:
“And there is life for you in retaliation,
O men of understanding,
That you guard yourselves”
Citizens cannot be safe unless the murderer is permanently removed from society. One who has deliberately killed once would likely not hesitate to kill again. And again. Especially in a system that only imprisons. While there are cases where an innocent has been incarcerated, those who are guilty without doubt are to be executed. Forgiveness to incorrigible offenders is not mercy; it is stupidity.