For anyone used to the typical debates that go on between “atheists” and “theists” in the world today, Moltmann’s take on this topic can seem a bit out of place. He frequently says something to the effect that “without Jesus I would not believe in God” (for example: here). While he has his own brand of natural theology (exemplified especially in God in Creation), he does not attempt to “prove” God’s existence through the cosmological arguments. After all, the “God of the cosmological proofs of God could not suffice for the new horizons of an open, explorable and changeable world.” (Science and Wisdom) So, when Moltmann talks about “protest atheism”, he is not talking about the same type of atheism that is typically set up in debate with Christian apologists:
Crude atheism for which this world is everything is as superficial as the theism which claims to prove the existence of God from the reality of this world. Protest atheism points beyond both God and suffering, suffering and God, sets them one against the other and becomes an atheistic protest against injustice ‘for God’s sake’.
The Crucified God, 227