"Of course, say the true believers, religion rests on faith, not intellect. But if all you need to do to prove I am wrong is to have faith that you are right, then no discussion is possible. . . . It is only by resort to what the Roman statesman Cicero called 'right reason' that men and women can interact with each other amicably in a civilized society.
Many followers of religion feel that only their path can lead to salvation. They have tremendous faith in their own religion, but at the same time they feel other religions are wrong. Therefore, they can feel a necessity to convert others to their faith.