Some opposites of belief:
Disbelief, doubt, nonbelief, unbelief, dissent, uncertainty, distrust, mistrust, skepticism.
The opposite of something that is believed would be something known: fact, knowledge, truth.
disbelief, doubt, unexpected, uncertain, ambiguous
non-belifes
atheism
Yes, polytheism is the belief in multiple gods, while monotheism is the belief in only one god. They are considered opposite in terms of the number of deities worshipped.
belief, certainty, confidence, dependence, faith, reliance, trust
Unbelief is the absence of belief, a passive activity, and disbelief is the active opposition to belief.
The belief that the soul and body can't be separated. The opposite, which is the belief that the soul and body are separate, is dualism.
Polytheistic refers to the belief in or worship of multiple deities or gods. It is the opposite of monotheistic, which is the belief in a single deity.
Disbelief. Disbelief: Adj. Lit., does not believe.
Hypocrisy means saying one thing or holding a belief, and doing the opposite. The opposite of hypocrisy is honesty, straightforwardness, and sincerity.
The opposite of elitist would be egalitarian, which is a belief in equality for all individuals regardless of social status or wealth.
You could say atheism but this is not a complete answer. This is a difficult question to answer because not all religions have the same basis. For example is a religion is based on faith or belief the opposite would be a lack of faith or belief, if a religion is based on reasoning or logic then you argue the opposite is ignorance or lack of logic.