The only difference between a Monotheist and an Atheist is the the Atheist disbelieves in just one more God than the Monotheist.
Why would a person believing in just one God be more correct than a person believing in many Gods? The more the merrier, right?
You possibly meant some other kind of -theist?
The Monotheist believes in one God (usually 'Yahweh, or 'Allah' or 'The Trinity'). But he disbelieves in all the Roman Gods, the Greek Gods, the Hindu Gods, the Persian Gods, the Aztec Gods, etc, etc. Let's say, for the sake of argument, that our Monotheist disbelieves in 205 'other Gods'. Our Atheist can disbelieve in 206 Gods, one more than our Monotheist disbelieves in.
The difference though I think is at the core: the monotheist believes in the concept of a god, they just believe the others that people worship are false gods.
The atheist doesn't believe in the concept of a god at all.
