This.You really don't realize how much added sugar and starch is out there in the food supply until you start having to avoid it. Once you start reading every package label and researching every restaurant's nutritional information, you quickly learn that this is a serious problem.
You're quite right. There are a lot of sugars out there, and a lot more things that break down into sugars when they're digested. The problem is not so much the sugar/starch as how quickly it breaks down into glucose: if it breaks down slowly, your body has time to deal with it, but if it breaks down quickly, it calls for your body to produce a whole lot of insulin fast. My doctor told me that repeating these alternating jolts of sugar and insulin can lead to insulin intolerance and, eventually, diabetes. As agouderia pointed out, refined flours and sugars present a problem because they've been stripped of various nutrients that can slow down the process of breaking down the complex carbohydrates into sugar. Eating whole grain breads and cereals gives your body more time to digest these sugars and starches.I think the type of sugar and the context of the food/drink is really important as well.
What the whole 'sugar is the devil' debate in essence boils down to is neither news nor rocket science: Processed food is what is bad for you. Make your own food as far as possible from scratch. Then even cake is okay for you, because a home made cake with a good recipe contains only a fraction of the sugar an industrial cake does.
Anybody who knows anything about cooking will know:
In processed food you have 2 options as flavor carriers that at the same time stabilize the product and increase shelf life - fat or sugar.
After fat was outlawed in the 70's/80's in the cholestrol/heart disease/weight gain craze, food producers turned to sugar. Which for them had the agreeable side effect, that sugar was the even cheaper ingredient.
I don't believe in the option of banning sugar/starch in products by law, because food producers who want to make a profit will look for another cheap 'filler' in their processed food - with who knows which harmful effects that will have.
The only thing that helps is education, teaching people from childhood on about ingredients and nutrition, using consumer power to outlaw the worst offenders in processed foods.
It works for all sort of PC causes - why not for the actual product?