I think it’s fairly obvious that these days there is a greater overall tendency toward violent fanaticism among the world’s Muslims than among the world’s Christians, and those Christians who are the exceptions tend to be more isolated cases.
With Muslims, the debate seems to be “nature vs. nurture” as it were, but I don’t see why it can’t be both. I’ll leave it to others to argue that core Quranic doctrine lends itself to violence, but Islamic culture seems to have become rather hot-tempered and hair-triggered over quite a number of issues. For example, the Quran call upon women to “dress modestly”, but in practice, although it varies, women and girls are subject to extremely restrictive dress codes enforced with strictness that approaches… violent fanaticism. And of course there are these “honor killings” of women over the most trivial breaches of sexual morality.
It seems like religions–or ideologies in general–can sometimes get caught up a cycle where the various doctrinal points are enforced with greater and greater strictness. Perhaps they blame their current problems on the previous generation’s laxity, or come to believe that a fully “purified” and absolute expression is needed before the belief system will fully deliver on it’s promise (the Chinese Cultural Revolution also comes to mind).
At any rate, as the violation of a taboo such as on pictures of Mohammed becomes more and more unthinkable, it becomes more and more of an outrage if ever it is, and then it becomes inevitable that someone is going to get hurt.
The Quran does seem to place a great deal of emphasis on defending the religion from its enemies, and if you’re brought up to expect that you’ll do a lot of fighting against enemies, you’ll see enemies everywhere. And these days we see how common it is for groups to portray not just criticism, but the making available of alternative lifestyles as an attack on their ethnicity.
But add to all that the humiliation they say they feel due to the fact that, when their countries are not being ruled or dominated or invaded by Westerners, they’re being ruled by what they see as pre-Western puppets. They’re brought up believing that their culture is superior, then look around to see the decadent West has been running circles around them for lo these many years. In short, they’re losers, they resent it, and so they go apeshit with vengeance at the slightest provocation.