Do not forget that the permission to interpret scriptures as you like (more or less) was hard won with much bloodshed. Judaism and Christianity had to accept being "tamed" simply to survive. Islam has not yet been faced with the "learn to live like civilized people or go extinct" condition that the other two major Middle Eastern religions passed through.

Early Catholic doctrine said only priests could interpret scripture.

Despite this, early thinkers like St. Augustine, Thomas Aquinas, and others debated the meaning of life, scripture, and God openly.

Then came Martin Luther. He nailed his 95 Theses to the cathedral door at Wittenberg and changed the nature of Western Christianity forever. Luther called for lay people to be able to interpret scripture for themselves, even going so far as to publish the Bible in the local language (instead of only Latin as the Church insisted).

After much internecine warfare and bloodshed (as parabarbarian points out above), Western civilization was worn out and settled down into a multi-religious society.

Keep in mind that much of Europe's so-called "religious" wars were in reality wars for territory, economic advantage, succession, or just age-old conflicts resurfacing.

Islam has two major sects, Sunni and Shi'a, and mostly managed to avoid the violent religious strife that plagued Medieval Europe.

While there have always been conflicts between the two, the current all-out Sunni-Shi'a conflict is a relatively new phenomenon. The Iran-Iraq War was one of the first cross-national Sunni-Shi'a conflicts that turned into an actual war. Sunni-Shi'a violence is on the uptick in Pakistan, Afghanistan, Jordan, Egypt, etc.

ISIS may be the spark that ignites a simmering powder keg. ISIS is exploiting Sunni dissatisfaction with Shi'a governance in Iraq and Syria.

Only dingbats justify Islam in anyway. Especially with they are medieval. We are no longer in medieval times unless you are some isolated tribes somewhere. If you move around in modern times with your medieval beliefs you should be terminated with prejudice.

"Despite this, early thinkers like St. Augustine, Thomas Aquinas, and others debated the meaning of life, scripture, and God openly."

Saint Augustine is my hero for chastizing would-be evangelists for their ignorance of the real world - a lesson from 1600-plus years ago many refuse today:

"Usually, even a non-Christian knows something about the earth, the heavens, and the other elements of this world, about the motion and orbit of the stars and even their size and relative positions, about the predictable eclipses of the sun and moon, the cycles of the years and the seasons, about the kinds of animals, shrubs, stones, and so forth, and this knowledge he holds to as being certain from reason and experience. Now, it is a disgraceful and dangerous thing for an infidel to hear a Christian, presumably giving the meaning of Holy Scripture, talking nonsense on these topics; and we should take all means to prevent such an embarrassing situation, in which people show up vast ignorance in a Christian and laugh it to scorn. The shame is not so much that an ignorant individual is derided, but that people outside the household of faith think our sacred writers held such opinions, and, to the great loss of those for whose salvation we toil, the writers of our Scripture are criticized and rejected as unlearned men. If they find a Christian mistaken in a field which they themselves know well and hear him maintaining his foolish opinions about our books, how are they going to believe those books in matters concerning the resurrection of the dead, the hope of eternal life, and the kingdom of heaven, when they think their pages are full of falsehoods and on facts which they themselves have learnt from experience and the light of reason? Reckless and incompetent expounders of Holy Scripture bring untold trouble and sorrow on their wiser brethren when they are caught in one of their mischievous false opinions and are taken to task by those who are not bound by the authority of our sacred books. For then, to defend their utterly foolish and obviously untrue statements, they will try to call upon Holy Scripture for proof and even recite from memory many passages which they think support their position, although they understand neither what they say nor the things about which they make assertion." – De Genesi ad literam 1:19–20, Chapt. 19 [AD 408]