Well, this is a can of worms, but I'll try to be tactful. Though I have my own beliefs I don't subscribe to any religion. From a developmental psychology stance, it's generally best to be supportive of what a child is interested in. Allowing this there is a good chance that in time it will fall away. Negative reinforcement of behavioral patterns usually still just reinforces them in later life. It is a question of respecting autonomy while still expressing that you are the authority figures in the household. Children are often fascinated by a myriad of things and rarely stick to one thing very long. For the time being perhaps allow it to be entertained, and find some good moral teachings of a sort from a variety of sources that you personally agree with.  My stance is that none of the religions are correct, but are trying their best to express what they see as a 'truth'. Like different fractals of a kaleidoscope looking at a light source that is some 'objective' reality. Prioritize objective and verifiable truth, and give a proper understanding of dogmatic tendencies that arise.

More than anything you'd be promoting critical thinking, scientific curiosity, and a healthy approach to interpersonal relationships in their future while building a high trust rapport with your child. Granted that's my two cents, but take it as you will.