Again we see in Syria mass murder, the use of chemical weapons, torture, mass rape, again: Why?
As Sandro Magister points out for an answer we can go back to the 2006 Regensburg speech of Benedict XVI, we can state with the Pope Emeritus and the Emperor Manuel II Palaiologos, "Show me just what Muhammad brought that was new and there you will find things only bad and inhuman, such as his command to spread by the sword the faith he preached."
Both Christian and Islamic fundamentalism are dangerous, as is secular fundamentalism, it always leads to inhumanity. The Emperor continues, ""God is not pleased by blood — and not acting reasonably is contrary to God's nature. Faith is born of the soul, not the body. Whoever would lead someone to faith needs the ability to speak well and to reason properly, without violence and threats… To convince a reasonable soul, one does not need a strong arm, or weapons of any kind, or any other means of threatening a person with death…"
For Catholics revelation is about Faith and Reason; Reason, which comes from God and is God's gift to mankind is part of man's very nature. Faith without Reason is dehumanising, even Christianity when reduced to mere Fideistic Positivism, the mere following of rules, rather than its emphasis on worshipping God "in Spirit and Truth", in Jesus as being the Incarnate Logos or forgetting Paul's insistence that the Law brings death and the Spirit brings Life, can be dangerous indeed.
The problem with Islam is that the best man can hope for is to become abdullah, a slave of God, a slave of a God who commands and instructs, but who is actually as far removed from man as a man is from a microbe, whilst Catholicism insists that man can hope for 'divinisation', we can hope "to see God face to face", to become Sons. We believe that Grace transforms base fallen nature that distorts man's rational nature, it enthuses our very nature and transforms us. Islam does indeed believe in 'One God' but it is God who is distant. It is certainly a God who is merciful and who expects his creatures to be merciful if they are to expect mercy but the Christian God transforms. The difference is Grace. The difference is the doctrine of the Most Holy Trinity.
Human reason transforms, Islam in the Spanish pre-reconquest Convivencia, when Islam, Christianity and Judaism dwelt more or less happily together was an age in which Islamic scholarship embraced, preserved and eventually passed on to men like Aquinas the philosophy of the ancient Greeks. It is not by accident that Christianity rediscovers Aristotle and Plato in dialogue with a rational Islam. Today's problem is that contemporary Islam has lost its sense of the rational. Nostrae Aetate urges us to dialogue, Benedict's Regensburg speech was a model for blunt, frank and courageous dialogue, it is more necessary now than it was 50 years ago.
Catholicism unlike than secularism, which can only confront, can engage in dialogue with Islam but it strikes me that in the West especially but elsewhere too amongst Moslems there is a great hunger for a faith which is rational. In my 'dialogue' with Islam - talking with local shopkeepers and cafe owners and students - the more Islam identifies itself as irrational and bloodthirsty, the more tentative enquiries I find are made about Christianity.