It is quite simple, really, all gods are imaginary, mythological-beings whose "believers" alone misdetect through a process of confabulation and self-deceipt.
Ask a monotheist why they reject all other gods and goddesses but one, and apply the same criteria to theirs.
Supreme deities are supremely absurd things; described as being imbued with "supernatural powers" and other contradictory terms.
Even polytheists can be shown that their specialised deities are similarly dismissed by the very words used to describe them, and by objective evidence of alternative, natural explanations.
It will be a brave step forward for all mankind when the last vestiges of superstitious religions are affirmed soley by history books.
Greetz,
Q