Placebos work even when you knows it's a placebo though. Pointing out something is a placebo is important because many are at best overpriced scams (homeopathy) and at worst actively harmful (chiropracty). The culture behind many placebos is also rife with pseudoscience and advocates against seeking out genuine care, so you should ensure nobody gets invested into placebos past a certain point.

One can make an informed decision regarding taking placebos if and only if one knows it's a placebo, else one will be scammed and/or harmed.