"The ultimate example is homeopathy, which is perfectly safe because it contains nothing at all and therefore does nothing; good or bad."
I'd beg to differ: homeopathy is potentially lethal because it promises benefit beyond placebo, may prevent timely medical intervention.
( And, yes, given cash flow constraints, purchase of expensive homeopathic 'remedies' may preclude purchase of functional medication / treatment... )
FWIW, a 'friend of friend' made the mistake of praising her favourite homeopathic remedy's benefits within my hearing. Given the non-trivial cost, and the belief that such serial dilution (*) unto nowt wondrously enhanced its powers, I suggested it should work even better if not ingested, if simply left in bottle and carefully observed.
Then I suggested it should work if left in shop window and observed there, no purchase required.
Then I suggested it should work if imagined as seen in shop window, so available 'out of hours'...
She thought this was a wonderful wheeze.
By which time she realized what I'd done, I'd left...
;-)
*) Watching typical homeopath do serial dilutions is a singular torture for any-one who's done proper analytical pipetting...