I get what you're saying, but nutrition is probably not a great example because we know nearly nothing about it. It's not ok to lock someone in a room and force-feed them for years to get data.
Anyways, that aside, what's insane to me is that there is a nearly-simultaneous story of the Opioid epidemic and people aren't losing their minds over this.
It's possible to investigate whether diets produce beneficial results in subgroups even without having a proper general model of diet and nutrition.
It's analogous to investigating whether drugs produce beneficial results in people with X disease even without having a proper model of how exactly X disease works.
We don't know that pale-skinned Caucasians need different recommendations in this scenario. That's the point. We barely know anything about nutritional science, let alone what one specific race of people needs.
If you have no clue how sun exposure actually affects the body beyond "ow burn hurt", you don't have the necessary knowledge to begin creating highly specific treatments. What would you base the science on? There's no real foundation.
Anyways, that aside, what's insane to me is that there is a nearly-simultaneous story of the Opioid epidemic and people aren't losing their minds over this.