Or the groups or that did the wrong thing simply died, and what we are left with are the accidental randomly distributed beliefs that came about for no reason at all, but happened to be ones that weren't slightly more correlated with dying.

The example I like to use here is that it is often assumed that cannibalism taboos arise because people don't want to/don't like to eat other humans, or that doing so increases risk of disease. But 1. Meat is meat, especially once cooked 2. Have you _seen_ some of the stuff we eat? and 3. Instances of humans eating other humans still happen routinely in the modern world when people are hungry enough, though in some well documented instances they don't actively kill anyone for food.

I find a plausible alternative hypothesis to be that the innate (pre-cultural) disposition toward eating conspecifics is essentially random, and that cannibalism is actively selected against because human beings hate nothing more than the feeling of being prey. We kill everything and anything that is even remotely threatening to us. Groups _without_ the cannibalism taboo are thus much more likely to be wiped out as a result of virtually universal hatred and fear by any other group around.

"Why don't we eat the people we kill mommy?" -> "Because eating people is bad and you are more likely to get sick." vs "Because if we did everyone else would hunt us down and kill us and anyone who believed like us. Better to leave them be or bury them to show we are not predators."

There is probably an answer out there waiting to be found in a pile case studies and social science polls.

tl;dr It's the hunting not the eating.