Agreed. In some scenarios in the past, the notion of God might have been useful, but yet might not have been necessary. For example, during the barbaric age, when a powerful man could just kill a weaker man with his sword, when no one is around and steal everything, I can imagine one possible way to stop such act might have been invoking an invisible punisher god who won't accept evil acts. So, the idea of an invisible entity and heaven or hell might have been very useful. But now that we know better, and all it's bad consequences, and already established some good moral philosophy of what's communally good and bad, we can throw those ideas away.