The difference between people eating "bad" carbs then and now is that back then, they actually used up their glucose through physical activity. Nowadays most of us are physically inactive most of the day, so that glucose has to be cleared and turned into fat or it sits around doing damage. And we're eating more stuff than ever before, well... were, that means the pancreas have to work harder and the receptors are bathing in sugar all day long and stop responding like they should.