It’s wholly coherent (dare I say plausible) that we’d be better off not knowing certain true things. Vonnegut talked about the heartbreaking necessity of lying about reality. However, I am incredibly skeptical that it is ever actually a good idea to taboo true ideas. (By the way, I’m talking about “knowledge-that” not “knowledge-how,” i.e., knowledge *that* there is no free will is different from knowledge *how* to make a bio-weapon. I’m okay with taboos on knowledge-how.) My rejection of taboos on true beliefs can be lumped into three categories: “fragility,” “remedy,” and “entailment.”
People are curious. We tend to poke questions. It is not in our nature to leave a question alone. Is it really a good idea to base our lives, society, or ethics on something vulnerable to scholarly investigation and curiosity? (Things that we want to encourage most of the time.) This does not seem like a stable way to organize our life or society. “You can fool all the people some of the time, and some of the people all of the time, but not all of the people all of the time,” as one Northerner put it.
If you understand the problem, you can actually fix the problem. As technology increases, our ability to fix larger problems increases. The more we can understand something, the more likely it is we can fix it. And if we can’t fix it, we don’t have to waste time trying to fix it. Also, if we can’t fix it, we can build workarounds that mitigate the problem. It’s very unlikely that putting our fingers in our ears and going LA LA LA is actually the optimal solution.
Your beliefs aren’t islands. They are connected to a vast web of beliefs. If it’s central enough, a false belief can rot whole branches of your belief web. You might have thought that beliefs about when the soul entered zygote would have no effect on anything outside of theology. You’d have been wrong.