Pogo,
I think it has to do with the question of whether or not god will heal you.
You're right that you don't need to believe in the efficacy of the doctor's ministrations in order for those ministrations to work. However, you have to actually receive the ministrations in order to have them do anything. We can prescribe you the antibiotic you need to clear up the infection, but it won't do any good unless you take it and if I refuse to give it to you, then you won't be taking it.
The argument of mike the wiz is that if you don't have faith, god won't heal you.
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Rrhain
WWJD? JWRTFM!