The evidence is strong, and seeing one child with Foetal Alcohol Spectrum Disorder might be enough to shock anyone into thinking the risk is too high to take. I have known foster carers who have cared for babies withdrawing from heroin, and those whose mothers drank, and they will describe quite vividly the heartbreaking effects and all agree that alcohol has the most harmful and lasting effects. Of course many (most) people will get away with drinking during pregnancy, but for some people a relatively small amount of alcohol can cause a lot of damage. There's just no way of knowing how much is safe for each individual.
I think, as was said in the programme, we see alcohol as a foodstuff rather than the drug that it is. Withdrawing from heroin is unpleasant but it won't kill you. Withdrawing from alcohol can be fatal. That ought to tell us something.