The existence of a multiverse is an argument against a creator or creators. Because then we can explain the 'fine-tuned universe' idea, which is of course an important theistic argument. If there are (or were) multiple universes, our 'fine-tuned' universe is only one of many, and just happens to be 'perfect' because all other universes failed to be. An omniscient creator would not require multiple universes, it would get it right the first time.
