I think this is a key point that rational people and skeptics don't get. Pseudosciences and pseudotherapies don't work because they produce accurate results, they work because of the tremendous effort that believers put in them to make them work.
IMHO, skeptics could help believers much more if they instilled in them some common sense and safeguards to avoid the worst crooks and dangerous therapies ("buy as many Bach flowers as you wish, it's your money - just don't abandon your chemotherapy") rather than try to appeal to their rational sense ("don't you realize how ridiculous it is? It could never work!"). At least in personal interactions, it is more likely that the former will gradually succeed in educating them than the latter.