You’re flat out wrong. All carbs aren’t alike in how they are processed in our bodies and we really have only had a couple of generations of ready access to so many sugars and other simple carbs.
That is the nub of the problem.
All carbs become glucose and provide the body with 4 calories per gram. Yes, there are varying efficiencies, and yes, absorption does matter to a certain degree (GI/GL also matter). However, for the sake of this discussion, people get fat and suffer from diseases like metabolic syndrome, diabetes, etc. mostly because they're fat. The reason they're fat is because they eat more energy than they burn. It has very little to do with what they eat, and everything to do with how much they eat. It has been this way since forever.