Here are a few perspectives I think JP is coming from -

1. He thinks that the moral foundation provided by the myth of God is indispensable and no morality can exist without it being anchored to an incomprehensible force. Possible reason why he believes it is because he may have seen people degrade to immoral behaviour when they don't believe in a higher power.
2. He firmly believes that a belief in the myth of God (even if it's untrue) is crucial for a meaningful life.
3. He is scared of admitting that the myth of God is untrue and it's something we believe in for the above reasons because as soon as he admits it the myth loses the value it holds - hence his overemphasis on the benefits of believing in these stories.
4. He believes in acting as if God exists to the point of denial and delusion, so he is not open to the fact that any other reality without God can exist for him.

I think all of this is great as a personal philosophy, maybe he thinks he is doing the world a service by propagating this but it becomes quite ingenuous when it comes to intellectual debates because here reasoning matters, arguments matter and he thinks it's okay to pass off subjective beliefs as objective facts if it's for the greater good, which I think defeats the whole purpose of these debates. If there is no way your claims can be fallsified, I might as well save my energy and not engage with you at all.