I have been struggling with this question for a very long time. I have asked myself how come Muslim friends of mine use a verse from Qur’an “if a Muslim kills one man it is as if he kills the whole world” to condemn terrorist attacks and the killing of innocent people?
The verse is from chapter 5:32 and it states “Because of this, we decreed for the Children of Israel that anyone who murders any person who had not committed murder or horrendous crimes, it shall be as if he murdered all the people. And anyone who spares a life it shall be as if he spared the lives of all the people. Our messengers went to them with clear proofs and revelations, but most of them, after all this, are still transgressing.”Muslims all over the world use a tiny part of this verse to defend themselves, but they do not provide the full context of the verse. For example, if you ask them what they would consider a horrendous crime, you will be given a very long list, including anything and everything that does not fit in the structure of Islamic teaching and practices.If you read the very next verse in the same chapter you will see how easily all the world except the Islamic world can be described as a community (therefore Muslims all over the world called themselves UMMAH) that has committed horrendous crimes against Allah and Muhammad by being non-Muslims. This particularly includes the Western world.
Qur’an 5:33 “The just retribution for those who fight GOD and His messenger, and commit horrendous crimes, is to be killed, or crucified, or to have their hands and feet cut off on alternate sides, or to be banished from the land. This is to humiliate them in this life, then they suffer a far worse retribution in the Hereafter.”Western military attacks on Islamic countries are considered as direct combat against Allah and his messenger.
Conclusion: According to the majority orthodox Islamic teachers (scholars, mollanas, and Imams) If a Muslim is a true Muslim living according to the Qur’an he must not let the non-Muslim go unpunished. Islamic teachings of Mercy are limited to Muslims alone.