Human societies have developed over the years with trial and error. Taboos against a food can have a positive correlation with negative health outcomes when consuming that food.

So just because there is a taboo against a food group does not mean that it will definitely be bad for you. There is just a positive probability that it could be.

Taboos can also arise out of fashion and economics, irrational beliefs and moral considerations of a particular culture.

So when we see a Taboo, it is often good to analyze: could this taboo have arisen due to health issues (here pork is a good example because of the danger of tapeworm infection) ? Or could the Taboo have arisen out of cultural reasons e.g dogs/horses are beloved in many cultures so a taboo may have evolved that we shouldn't kill them.

> I'm reasonably certain the idea of certain food being taboo is almost completely due to cultural norms.

TL;DR: Sometimes it due to cultural norms and sometimes its due to negative health outcomes that get noticed due to trial and error over generations.