People are allowed to disagree with one another; disagreement is the event that occurs when people have differentiating viewpoints.
Both ends of the spectrum, religious and non-religious, project their viewpoints onto an oppositional side. Not that it is justified, but it is common. Non-religious people tend to lean towards saying that religion does not exist because of [specific reasoning], and religious people tend to lean towards saying that their higher power exists because of their beliefs. Neither side is ruled by objectively fact, because we simply do not know.