Homebrewing wine made me suspicious of the claim that beer/wine were drank because the water supply isn't clean. The first thing you do is sterilise anything that will make contact with the liquid or it will spoil and be poisonous.
When your must or wort gets contaminated due to lack of sterilization it's unlikely to become poisonous. It's more likely to become vinegar. It's the fact that you're using uncontaminated fruit juice or boiled wort that makes the beer or wine safer to drink than water out of the cistern beside the outhouse.
Maybe it helps that you sterilize a big batch once and then it stays safe indefinitely? I'd rather drink a 2 year old bottle of wine than a 2 year old bottle of lake water.
As a consumer one does not have to sterilize though, and that would be the advantage. That it tends to spoil very badly when not sterialized can be seen as a feature, it may act a detector for bacteria.
It will not be poisonous. It will just taste sour.
You don't sterilize, you sanitize. There's a big difference.