We valorize the right to say anything we like, and they valorize the right to kill anyone who says insulting things about religion. We insist our right is right and theirs is wrong, because...? Killing is worse than humiliation? Not to them it isn't, because they have honor, something that once was a great motor of human behavior, and which we have almost entirely lost. They look at our blithe and widespread insults toward Christianity and conclude that we have no real faith, and are worthy of no respect. Because we have no honor, as they understand it, our guys get killed in Afghanistan by their supposed allies. We just don't get it.
The Enlightenment was what helped to kill honor. Voltaire was beaten up by the coachman of a marquis he had lampooned, and this is taken as a signal event in the development of Voltaire's commitment to free speech. OTOH, Shakespeare was never beaten up, and he wrote some pretty good stuff. Maybe there's something good to be said for circumspection, although now we call it self-censorship and it is a Bad Thing.
We believe that if speech is free, the truth will eventually emerge. This is a faith unsupported by evidence, and false on the face of it, since at every instant of history what we regard as truth is subject to revision by truthier statements. The truth actually never emerges, but we wait for it in hope, just like Christians wait for the Last Day.
Every belief has its downside, including Enlightenment freedoms. Give any religion enough shocks from blasphemy and it collapses, and then where are you? Left with only the belief in fame, sex, power and money, which no one dares to challenge, because the basis for challenging it has been destroyed. And do we like the world thus created? Plenty of people in the Muslim world don't.
I think it's significant that the most successful terrorists are not ignorant farm boys but educated men well engaged with the west. They've seen what we have to offer and have rejected it, and this baffles us. Are we not the supreme achievement of human culture? Is it not obvious, for example, that the point of all culture is the accumulation of capital and that any misery attendant on this process is therefore justified? Isn't it obvious that the powerful are free, under Enlightenment rules, to heap any scorn they choose onto the weak, or the outsider, and the only response allowed to perpetual humiliation is a counter-insult? A tract?
Another result of Enlightenment theories of free speech is the collapse of manners. We behave like brutes, secure in the knowledge that we will never be physically called to account for anything we say or publicize. (Movie fantasies excepted: assholes in the movies are invariably physically punished. I think that's significant.) Except we can't say anything bad against the historic subjects of bigotry, or in favor of sex with anyone under age 18 and we can't upload a secretly-taken video of two gays making out. Or use racial epithets in public. But it's perfectly okay to shit on the deeply held beliefs of half a billion people--totally cool, in fact, and how naughty of them to object!
I'm immersed in the world of honor now, in my book, and am exploring the transition between that world and the money/politics-dominated world we live in today. The old regime had its problems, sure, but there was something satisfying about the ability to make someone's body responsible for the output of their mind. Most of the world still thinks it's absolutely okay to kill a writer if they don't like what he writes. Of course, we have to deplore that. We think it better to starve a writer rather than shoot him in those circumstances, but be that as it may, there is something noisome about the paparazzi, about the tabloids, about the anonymous posting, YouTube world we have created. The myth is that total freedom is necessary for art and literature to thrive; in fact, a huge proportion of the works we cherish were written by people who had no rights of free expression at all.
A complex issue here.
I've just finished reading Der Brand, the story of what the air war of 1940-45 was like from the German point of view. It was the great working of nemesis in our time: as Germans were asphyxiating and roasting children in Poland, the RAF was asphyxiating and roasting the children of those Germans at home. Makes one proud to be human. I wonder what nemesis is being prepared for us, for although the Germans killed more foreign innocent civilians than any nation in recent history, we are number two, a fact not generally spoken by our leaders.