Here’s a discussion on religion and bigotry. For a more detailed analysis of religiophobic bigotry, consider reading my article on the topic, found here. There are also a whole bunch of books on the anthropology of religion, many of which can be found on Amazon. Overall, religion has not been shown to be harmful. It does not make sense, from the standpoint of evolution, for religion to survive if it is harmful. Religion is not a delusion. A delusion must be contrary to one’s cultural understanding. Religion is not. Of course, science is useful, and criticizing religion should be done using a valid scientific framework, something which is usually not done. And finally, there’s no more justification for calling religion a disease or a mental illness, than there is for calling homosexuality one.