Argument from wishful thinking. The primary psychological role of traditional religion is rationalizing the tragedy of death as a good thing to alleviate the anxiety of mortality.
“I would love to believe that when I die I will live again, that some thinking, feeling, remembering part of me will continue. But much as I want to believe that, and despite the ancient and worldwide cultural traditions that assert an afterlife, I know of nothing to suggest that it is more than wishful thinking. The world is so exquisite with so much love and moral depth, that there is no reason to deceive ourselves with pretty stories for which there’s little good evidence. Far better it seems to me, in our vulnerability, is to look death in the eye and to be grateful every day for the brief but magnificent opportunity that life provides.” – Carl Sagan
What's that to do with God exists or not. You mean the existence of God or not depends how humans behave?