Why does the Shafi'i Madhab permit killing all non Muslim adult males during Jihad?

Why does the Shafi'i Madhab permit killing all non Muslim adult males during Jihad? Is it just because of their disbelief? Isn't that too cruel? **Bidayat al-Mujtahid** Ibn Rushd writes: > They disagreed about the case of hermits cut off from the world, the > blind, the chronically ill, the old who cannot fight, the idiot, and > the peasants and serfs. ... **According to al-Shafi'fs most authentic** > **opinion, all of these categories (of people) are to be put to death.** > > The Distinguished Jurist's Primer Vol. 1 p. 458 translated by Imran > Ahsan Khan Nyazee Ibn Rushd writes elswhere: > The basis for their disagreement stems from the conflict of the > specificity in some traditions with the general implication of (some > verses of) the Qur'an, and also the generality of the authentic saying > of the Prophet (God's peace and blessings be upon him), "I have been > commanded to fight mankind until they say, 'There is no God but > Allah.'" The words of the Exalted, "Then, when the sacred months have > passed, slay the idolaters wherever ye find them", **imply the slaying** > **of every nonbeliever** **whether or not he is a monk**, and so does the > saying of the Prophet (God's peace and blessings be upon him), "I have > been commanded to fight mankind until they say, 'There is no God but > Allah'". > > The Distinguished Jurist's Primer Vol. 1 p. 458-459 translated by > Imran Ahsan Khan Nyazee **Al-Hidayah** > A woman, minor, enfeebled old man, an invalid, and a blind man are not > to be killed. ... **Al-Shafi'i (God bless him) goes against our opinion** > **in the case of the enfeebled old man, the invalid, and the blind. The** > **reason is that permitted killing in his view is based upon unbelief** > > Al-Hidayah Vol. 2 p. 293 translated by Imran Ahsan Khan Nyazee **Reliance of the Traveller** > **It is permissible to kill old men ... and monks.** > > Reliance of the Traveller o9.10 translated by Nuh Ha Mim Keller **Follow Up Question** Does this mean that not all non combatants are impermissible to kill?