People are still getting nerve damage from too much vitamin B6 in energy drinks and vitamin supplements, and that's a well known and widely taken vitamin. The idea that you can take experimental drugs your entire life at little risk is optimistic.

I had no idea. At points in my life I consumed a lot of nutritional yeast.

Surprisingly, many people seem to think that pushing a few random pills into a machine optimized over some million years of evolution will tune it so it works better. Go figure...

It works for the majority of modern medicine, so it's not all that black and white.

Yes, although even for modern medicine curative and preventative strategies are very distinct. Sure, they'll give you pills to compensate for a problem you already have. But there are few meds that protect you against stuff you'll maybe catch in the future. Vaccines and antibiotics are obvious examples, but I'm not aware of many others. The rest of preventative strategies overwhelmingly consists in correcting deficits or excesses (calories, vitamins, sleep, exercise etc.)