Someone once said the reason we had alcohol before civilization is that we carry around a chemical testing laboratory in our faces.

It just so happens that everything in beer that can go wrong and hurt you (any sooner than cancer) creates a distinct aftertaste and you can learn to avoid it rather easily.

The only exception of course is if you use poisonous ingredients in the first place.

or instdad of ethanol have brewed methanol.

That's much more of a danger when distilling, just brewing with yeast it's difficult to wind up in a situation with dangerous methanol.