First, experts usually don’t know nearly as much as they think they do. Experts often get it wrong, thanks to their inherently irrational brains that, through overconfidence, bubbles of like-minded thinkers, or just wanting to believe their vision of the world can be true, mislead us and misinterpret information. Rationality is subjective. All humans experience such biases; the real problem is when we forget that scientists and experts are human too—that they approach evidence and reasoned deliberation with the same prior commitments and unspoken assumptions as anyone else. Scientists: They’re just like us.
And second, science has no business telling people how to live. It’s striking how easily we forget the evil following “science” can do. So many times throughout history, humans have thought they were behaving in logical and rational ways only to realize that such acts have yielded morally heinous policies that were only enacted because reasonable people were swayed by “evidence.” Phrenology—the determination of someone’s character through the shape and size of their cranium—was cutting-edge science. (Unsurprisingly, the upper class had great head ratios.) Eugenics was science, as was social Darwinism and the worst justifications of the Soviet and Nazi regimes. Scientific racism was data-driven too, and incredibly well respected. Scientists in the 19th century felt quite justified in claiming “the weight of evidence” supported African slavery, white supremacy, and the concerted effort to limit the reproduction of the lesser races. It wasn’t so long ago that psychiatrists considered homosexuality unhealthy and abhorrent. There is at least one prominent, eminently rational psychiatrist who hasn’t come around on transgenders. And many scientists decided that women were biologically incapable of the same kind of rationality you find in men, a scientific sexism reborn in contemporary evolutionary psychology. Weirdly enough, you find a similar kind of misogyny in that high priest of scientism, Richard Dawkins.