Ted Kaptchuk of Harvard Medical School studies placebos | Harvard Magazine Jan-Feb 2013.
One of the most intriguing points was that even a placebo identified as such to the patient can have a beneficial effect. So perhaps whatever benefit people derive from religious rituals does not require insistence on actual belief from the participants.
On the other hand, the subjective relief from the placebo (even when not identified as such) is apparently usually not matched by any objective improvement in the actual pathological condition. (The mental effects may have objective manifestations in brain chemistry or whatever of course, but the underlying illness and physical damage continues to progress.)
Masking pain, or feeling good about life, can be a valuable goal but should not be allowed to divert attention from effective treatment of a curable illness – or from giving effective attention to the ills of the world around us.