We find ourselves in a clash of civilizations. On the one hand, we have the progeny of the Enlightenment. Despite our flaws, humanity has achieved unthought-of progress as a result of these ideals. On the other, we have fundamentalism characterized by our worst impulses: profound immaturity evidenced by the "you insulted me so now I'll hurt you" behaviour of these people, as well as unthinking supplication to unworthy authorities and adherence to their dictates.
It's worse than that, though. The people who called for and carried out this attack and others like it were not seeking to hurt those who insulted them. Rather, they perceived some offense and so struck out blindly, murdering innocents. This is the very height of immaturity. It is supremely childish, and is behaviour that would be distressing even in a toddler. This is what fundamentalism reduces us to: unthinking animals frothing at the mouth and indulging in our most base tendencies. It strips us of all semblance of civilization, and in so doing degrades the species as a whole.
These two paradigms, civilization and barbarity, are utterly incompatible. They cannot coexist. The unfeeling cruelty engaged in by these fundamentalists is anathema to the very foundations of our society and the human progress it engenders. Where the two cultures meet they will inevitably clash, inevitably with violence.
We must decide whether our values are worth fighting for. Education and economic liberation can only take us so far. Where the scions of hatred and ignorance come at us with arms, we must be prepared to respond in kind, or lose what our forebears fought for.
We were all once barbaric (in many, many ways, still are). How did we get out of it? Education, not by some enlightened assholes blowing us up. Please take a step back from your emotion and think about what you're saying.
Again, we didn't start this fight and we cannot coexist. This is not a matter of live and let live, as they won't let us live. The fundamentalists are expansionist, and are not happy unless everyone believes as they do. Take this attack, for instance. In Islam, you are forbidden from insulting the Prophet. Fine. If you're Muslim, then don't insult the Prophet.
That's not enough for them. They want everyone else to follow their dictates, too. Where they are not followed, these people think it entirely reasonable to murder innocents unconnected to the original "offense". Our only options, here, are to either respond with force or acquiesce. If we choose the latter, we have abandoned our values of free speech in favour of their values of adherence to their dogma. This cannot be.
Of course there is no one "Enlightenment" to point at - but the point is that one can take reason too far, to the point it has the same effect as religious extremism: "you are logically wrong so I'll hurt you".
Ultimately the point of many religious faith is a constant reminder we are all fallible and do not have access to absolute truth. Many fundamentalists forget this, preferring to focus on morality over faith.