God is not a minimalist explanation of natural phenomena, so science rejects God outright for that. That means there is no observed and proven natural phenomena that could not be more simply be explained without God. He is, however, an alleged actor in nature, so within the domain of science. Therefore anyone who accepts the scientific method as a proper approach to determining what one should believe, should not believe in God.
It's difficult to ague with conviction whether anything exists or doesn't exist without establishing a framework for determining when it is reasonable to believe something exists. The scientific method provides one such framework, but a theist may reject it as an approach for establishing the state of existence of God. So in order to argue about the existence of God we must first establish a framework for how to prove thing exist or don't exist that we agree on.
It's difficult to ague with conviction whether anything exists or doesn't exist without establishing a framework for determining when it is reasonable to believe something exists. The scientific method provides one such framework, but a theist may reject it as an approach for establishing the state of existence of God. So in order to argue about the existence of God we must first establish a framework for how to prove thing exist or don't exist that we agree on.