If nobody believed in superstition it would be unable to hurt anyone
Why not say household bleach cures cancer and autism
and just about anything?
If you believe in the miraculous, you can say then that it is possible that household bleach can cure cancer if you drink some for three days.
The placebo effect can fool anybody into thinking a treatment works when it is in fact useless. And bringing in the supernatural into it is a placebo in itself. You get hope from the thought that the laws of cause and effect may not apply in your case and your illness may lessen or vanish which is not the norm. You get hope from feeling that God is going to miraculously cure your toothache and let children die of cancer - you feel that special and that important.
What if proof appears that the treatment is dangerous? Argue that there are testimonials that say different. You will always have testimonials anyway no matter what kind of rubbish medicine you put out. Argue that many medical treatments were controversial and poorly understood for years and then were endorsed by the medical professionals. Blame the drug companies for creating scepticism towards the treatment you have invented. Argue that the bleach works best if people use it secretly and that if anybody gets sick and dies it is not down to the bleach but some unknown factor. Perhaps the magic has a reason for letting the bleach cure one person and not another? Chances are you will say, "Look it did some people good so it works. Those who died after taking it did not have enough faith or it let them die for it was for the best in the divine plan".
You can ignore research that says it could kill you or permanently injure your body. You could say that it is talking about bleach that does not have the miracle power or say that bleach from now on has the power so the research doesn't apply. Anyway to believe in miracles, you have to put aside the research that says for example some illnesses cannot just disappear. They do when magic makes an input.
Notice how people will eventually see through it if you blame the drug companies. They will also see that though it is true some treatments that work have been condemned by medicine, that medicine will discern the truth in time. Time will tell but if a treatment is scoffed at by the medical professionals for long enough it will become clear that the treatment really is useless. Notice how once you bring "mysterious divine purpose" and the supernatural into it there is no limit to the things you can say to give the impression that an ineffective treatment is effective. Get a few testimonials and people will fall for it.
Anybody can be detached from reality. We all suffer that to some extent and some more than others. But nothing makes the bubble you put yourself in harder to burst than religion. It gives you infinite ways to excuse the inexcusable or to believe utter shite.
If you really believe in the miraculous, you will not object to the person who says bleach has miracle powers. You will say, "Maybe it does!" Or, "She has a right to her religious opinions even if they are not the same opinions as myself." Actions speak loudest.