The basic problem is that a religious moral code is almost always tied in to what happens in the next life (should there be one). This means that anything that happens here can be excused in terms of the value it gives there. In other words worrying too much about the next life can make you callous to what happens in this one. Generally though religions do not sanction killing they can excuse it. Moslems have the concept of Jihad, the catholics have a roving excuse called "Duel effect" which means that if you cause evil events whilst trying to do good sometimes its ok. (and sometimes not). Most religions have been guilty of this at some point.
What it boils down to is that religions, like anything else, can be used as an excuse to do what you like. ( "it was the drink", " the devil made me do it", "I come from a broken home" etc. etc. etc.) Much though I would like to ban all forms of religion out of spite, it has to be said they really arent responsibe for the things done in their name.