Without a moral God, reality can be suspended; unborn babies can become “products of conception,” Men can marry men and women can marry women. Men can BE women and women can BE men. Without a moral God, man makes up the rules.
Without agency, we are not human. If we are not human, but mere bundles of sensations and appetite, then anything is permissible, and a cosmos where anything is permissible is a cosmos of darkness, chaos, and oblivion. For Atheists to doubt the existence of God, they must in turn doubt that they exist at all.