Why must we always become skeptics by default? If it works, who cares whether or not it is a placebo?
The placebo effect is basically the Hawthorn Effect (my favourite effect). That means as long as you think someone cares you will feel a bit better.
Now, if you were in receipt of the Hawthorn Effect and applied critical thinking to the positivity you felt you may well lose the effect.
That's why you should never apply critical thinking to ones god of choice.