The Real Problem With Religion

"The real problem is not that those who stop believing in God will believe in anything, but that those who have faith in God can justify doing anything." Simon Morris
How can one rationally explain killing "infidels' or "sinners" and yet claim their religion is one of peace or love? We have heard the so-called joys of being a Christian or Muslim over and over. These two major religions worship and quote from the same god, but yet they are enemies of each other. They are enemies because they both want to conquer and rule the world. If "love" and "peace" were their true message then why do they kill in the name of their "God" or "Allah"? Why do they force their religions upon uninterested fellow beings?