Prominent individuals in psychology have stated or implied that religion is a delusion. These people are often delusional themselves. I have explained why religion is not a delusion or mental illness in “The Pervasive Nature of Religiophobia” and “Religion is an Illness and Evolution is Wrong (Not).“
In these articles, I have explained that a delusion requires a perception of reality which is contrary to the cultural understanding of the perceiver. Those who believe that “god is talking to them” or has left a sign believe this because their cultural upbringing has taught them to interpret sensory information in that way. But people like Richard Dawkins have a different cultural understanding of the world. Their understanding is one based purely in mathematics and science. If the current scientific body of evidence points in a specific direction, that is what is interpreted as being “true” and if current theory and evidence contradicts a position, that position is interpreted as being false.
So what is happening with Dawkins and others like him call religion a delusion or mental illness? In order to make this claim, their perception of reality must be different from the current body of scientific theory and evidence on the topics of mental health and the anthropology and psychology of religion. Their perception contradicts the cultural understanding of reality. By the definition of delusion then, Dawkins et al. are the delusional ones.
So while “religion is a delusion” is wrong, or at least inconsistent with current scientific understanding, that thought process is delusional itself. It is ironic, but it is not surprising. In some ways, these people, who are clearly Religious Rejectionists, have two very different domains of thought: their mundane thought processes, which center around science, and their religious thought, which is centered around the belief that there are no gods, afterlives, etc. It is the latter domain which other religions contradict and therefore result in the conflict which drives them to make the claims that they do.