This argument couldn't have been more wrong: the lesson of today's terrorism is that if God exists, then everything, including blowing up thousands of innocent bystanders, is permitted — at least to those who claim to act directly on behalf of God, since, clearly, a direct link to God justifies the violation of any merely human constraints and considerations. In short, fundamentalists have become no different than the "godless" Stalinist Communists, to whom everything was permitted since they perceived themselves as direct instruments of their divinity, the Historical Necessity of Progress Toward Communism.In my opinion, this summarizes the basic problem with any religion that claims to have an exclusive line on what constitutes "God's will" or even what is supposed to be fundamentally right. You don't need any god's permission or approval or some promise of salvation to be good. You can perform a good deed, help your neighbor or a stranger, and live a moral life in general simply because it is the right thing to do. It's not rocket science.
By the way, the "defenders of the faith" to whom Zizek refers are atheists.