I am not a scholar of Islam, or anything else, but what I believe is that Islam is a valid religion created by God for the salvation of souls. Valid religions are created by God to suit different temperaments. Each and every religion created by God goes through ebbs and flows of proper adherence by people. Hence Buddhism has been in a state of moral decline for hundreds if not thousands of years while Chistianity has been for a few decades. Hence there are Middle Eastern cities where anything and anyone is for sale, such as Baghdad, which had a long-time reputation as a dirty, disgusting city, but not always so. Perhaps we can point to supposed violent passages in the Qur'an; as in the Bible there may be individual passages which suggest a violence and bloodletting as proper usages of religion. Luckily in Christianity the Church alone has the responsibility to authoritatively interpret Scriptures, and as we are well aware there are divisions within Christendom where that authority is usurped to the detriment of indeed the entire world.
I am reminded of the Red Pioneers, basically a Boy Scout-type organization promulgated by murderous Marxist-Leninist-Communists in Russia, where they were seen as wholesome and harmless and patriotic. Generations of youths in Russia were raised in this organization, and indeed anything said against the Soviet system was seen as an attack on patriotism, Boy Scouts, and motherhood, but really the root of their society was in this murderous Communist ideology. The Russian people often times just didn't know any better, since their press was so controlled. I see a lot of the fanaticism in the Middle East the same way. There are generations of youths being taught to hate Israel and America, and anything which underscores the invalid observance of their valid religion is seen as an assault on their patriotism and way of life, albeit through the proxy of their religion, which few really adhere to in a serious way anyway.
Few of today's observant Muslims would have the ability to understand the Islamic success of a Hussein al-Hallaj, much as most Christians today would have no understanding of the Christian success of a St. Germaine or St. Francis of Assisi, much as most Hindus today would have no understanding of the Hindu success of a Sri Ramakrishna.