Here's an intriguing little argument sketched by Graham Oppy:
The only kind of freedom that it is possible to have is compatibilist freedom. But it is impossible to have compatibilist freedom if there is a causally upstream agent who selects one’s beliefs and desires. So it is impossible for you to be free if you are one of God’s creatures. But freedom is a highly significant moral good. So God’s non-existence is morally desirable: God’s non- existence is necessary for our freedom and the goods that our freedom makes possible—e.g., moral responsibility.
Oppy, "Arguments for Atheism", in Oppy Graham (ed.). The Oxford Handbook of Atheism (OUP, 2013), p. 59.
