Can the well-documented placebo effect in medicine be applied to the comfort religious belief gives many? In the case of religion, should such an affect be encouraged, discouraged, or dismissed?
You could argue that none of us will ever know until we die, and if we were wrong in being religious we will never know we got it wrong. If various monks or nuns in various religions (to take an extreme example of devotion) got it wrong - and some would have to have had if you subscribe to the logical view that only one religion can assure you an afterlife, what possible advice can be given?
If you feel someone is wasting their life on a misguided religious quest should you just preserve silence, salute the meaning it lends their life and leave well alone? What duty do we have here, if any? Philosophers understand the points involved better than most and can see through many misconceptions in religious belief that believers are unaware of.
Each-to-his-own is surely a tragic cop-out.