The American Indians in South America, ate potatoes for hundreds of years, potatoes, even saved many people in Europe there’s nothing wrong with them in moderation.

those potatoes aren't like the ones we cultivate now; similar for things like corn and bananas.

and they weren't eating half a kilo of them, deep fried, in a sitting (e.g. fish and chips or McD's french fries) for breakfast lunch and dinner

They also had a much more active lifestyle (e.g. farming, hunting, physical training, etc.) that would offset carb heavy foods.