1. It is justified to fight against believing Muslims, because there was fighting among early Muslims.
2. After defeat of USSR the Jihad in Afghanistan was not against USSR or USA, it was against the Muslims of Afghanistan, the Mujahedin who had fought against USSR. This was justified through Fatwas by Ulema [Islamic Scholars] on the grounds of implementation of Shariah rule in Afghanistan. If Jihad was justified against pious Mujahedeen of Afghanistan, why it is not justified against people of Pakistan who are neither Mujahedeen nor scholars of Islam?
If some non Muslims would have given such logic to justify mass murders, one might excuse him being ignorant, but such argument from those claiming to be pious and learned Muslims reflect nothing but their total ignorance to Quran, Sunnah & Islamic history. Keep reading >>>