There was enough pre-existing theory to suggest that vitamin D could be beneficial, and enough preliminary data suggesting that it was beneficial, that several government bodies and public health officials did strongly recommend mass vitamin D supplementation as a low risk intervention. Aside from that, some places already supplement milk with vitamin D because the effects of insufficiency have been known for many decades.

The language of uninformed skepticism really bothers me. Using terms like "quack science" and "crank". What does that do? It just heaps stigma into an already complex and messy conversation that really needs nuance, thoughtfulness and care.

For what? To distinguish yourself as smart? To me that kind of language just comes off as reductionist.