This is an obvious logical fallacy. Firstly, evil is not solely caused by religion or God or any one thing in particular. It is more likely that it is to do with the psychology of human beings. Why a human being would commit murder in the name of God is not down to his religion. As of yet, there is still no explanation as to what would make people kill. What would be gained from such an act. For example, the fighting over land is due to human greed not the belief in God. The wars, terrorists etc. are all due to human needs, competition over one another etc.
Next, we do not reason every single action we do in our minds before doing them. A lot of the things we do are not fully reasoned out. Thus, rationally thought out morals would not work in many circumstances. Rather, to be good, we need to use our conscience that is inherent in everyone.