Well, killing all blasphemers regardless of what religion or gender they are is NOT established Sunnah. There is no Sahih Hadith which prescribes mandatory death penalty for all blasphemers. And that's why different schools of Islamic jurisprudence prescribe different punishments for blasphemy. Blasphemy committed by Non Muslims has always been considered a pardonable offense by the overwhelming majority of ulema.
295 - C of Pakistan Penal Code mandates death penalty for all blasphemers regardless of what religion or gender they are .... This is against the Hanafi, Shaafi, Maliki and Jafari jurisprudences ... Only Hanbali jurisprudence, followed by no more than 2% of Muslims, holds similar views regarding Blasphemy punishment. But even the Saudis have pardoned blasphemers (Sabri Bogday for example)
Hanafi – view blasphemy as synonymous with apostasy, and therefore, accepts the repentance
of apostates. Those who refuse to repent, their punishment is death if the blasphemer is a Muslim man, and if the blasphemer is a woman, she must be imprisoned with coercion(beating) till she repents and returns to Islam.3 If a non‐Muslim commits blasphemy, his punishment must be a tazir (discretionary, can be death, arrest, caning, etc).4,5
Maliki – view blasphemy as an offense distinct from, and more severe than apostasy.Death is mandatory in cases of blasphemy for Muslim men, and repentance is not accepted. For women, death is not the punishment suggested, but she is arrested and punished till she repents and returns to Islam or dies in custody.6 A non‐Muslim who commits blasphemy against Islam must be punished; however, the blasphemer can escape punishment by converting and becoming a devout Muslim.7
Hanbali – view blasphemy as an offense distinct from, and more severe than apostasy. Death is mandatory in cases of blasphemy, for both Muslim men and women, and repentance is not accepted.8
Shafi’i – recognizes blasphemy as a separate offense from apostasy, but accepts the repentance of blasphemers. If the blasphemer does not repent, the punishment is death.9,10
Ja'fari (Shia) – views blasphemy against Islam, the Prophet, or any of the Imams, to bep unishable with death, if the blasphemer is a Muslim.11 In case the blasphemer is a non‐Muslim, he is given a chance to convert to Islam, or else killed.12
2 Sahih al‐Bukhari, 3:45:687, Sahih al‐Bukhari, 5:59:369
3 Abu al‐Layth al‐Samarqandi (983), Mukhtalaf al‐Riwayah, vol. 3, pp. 1298–1299
4 Ahmad ibn Muhammad al‐Tahawi (933), Mukhtasar Ikhtilaf al‐Ulama, vol. 3, p. 504
5 P Smith (2003), Speak No Evil: Apostasy, Blasphemy and Heresy in Malaysian Syariah Law, UC Davis Journal Int'l Law & Policy, 10, pp. 357‐373;
6 D Jordan (2003), Dark Ages of Islam: Ijtihad, Apostasy and Human Rights in Contemporary Jurisprudence, The.Wash. And Lee Race and Ethnic Anc. Law Journal, Vol 9, p 55‐74
7 Carl Ernst (2005), "Blasphemy: Islamic Concept", Encyclopedia of Religion (Editor: Lindsay Jones), Vol 2,Macmillan Reference, ISBN 0‐02‐865735‐7
8 Abdullah Saeed and Hassan Saeed (2004), Freedom of Religion, Apostasy and Islam, Ashgate Publishing, ISBN978‐0754630838
9 L Wiederhold L, Blasphemy against the Prophet Muhammad and his companions (sabb al‐rasul, sabb al‐sahabah): The introduction of the topic into Shafi'i legal literature, Jrnl of Sem Studies, Oxford University Press, 42(1), pp.39‐70
10 P Smith (2003), Speak No Evil: Apostasy, Blasphemy and Heresy in Malaysian Syariah Law, UC Davis Journal Int'lL aw & Policy, 10, pp. 357‐373
11 Ayatullah Abu al‐Qasim al‐Khoei (1992), Minhaj al‐Salihin, vol. 2, pp. 43‐45
12 Ali ibn al‐Hussein al‐Murtada (1044), Al‐Intisar, pp. 480‐481