A pregnant woman can rationally and morally choose to have a drink every once in a while —- there’s almost no chance there will be a problem, while at the same time, it’s a rational and moral for doctors to recommend not drinking at all — millions of lives are at stake potentially.
On my own review of pre-natal diet recommendations, in my view the issue is about risk management rather than etiology of disease. for instance, my wife and I often joked that if we ate according to our countries health recommendations, we'd never eat out and only eat heavily processed foods, because it was the only place where the risk of various poisonings were near 0. But in practice, home kitchens aren't risk free, nor is or own non professional food prep or diet selection. And the mother needs to balance off sufficient variation in diet to be balanced and healthy, opportunity cost of other beneficial actions towards her and the child, etc, all of which are not accounted for, because science and medical research are not policy oriented documents. And it must be said that the relative risk of many of these things is very small from a clinical point of view.