[smeej]

I think people get away with that kind of thinking more easily when the intervention being proposed seems generally unobjectionable anyway.

"Correcting vision problems for older adults" sounds like a good idea in its own right, so when someone adds a "and maybe it'll reduce dementia!" thought to the equation, even though the relationship might very well not be causal, people kind of shrug out a, "Sure, that'd be nice," in reply.