All religions have their accepted dogma, or articles of belief, that followers must accept without question. This can lead to inflexibility and intolerance in the face of other beliefs. After all, if it is the word of God, how can one compromise it? At the same time, scripture and dogma are often vague and open to interpretation. Therefore, conflict can arise over whose interpretation is the correct one, a conflict that ultimately cannot be solved because there is no arbiter.
Besides, believing in something that isn't real is just plain mental.