I have thought about this too. It would be bizarre if all of us thinking "they're working on that" had some kind of society-wide placebo effect to actually cause people to live longer and healthier.

Now that's a self-reinforced feedback-cycle I can get behind!

I think this way of thinking is rather new, especially considering how many more people believe this than 100 years ago. Back then modernity was in full rising force, so there certainly was a social notion of progress happening to everything on a wide scale, and expectations of Western civilization's eventual achievement of some kind of utopia. But back then they were so limited by what they didn't even know about, so their vision of what modernity would become pales in comparison to what post-modernity actually has been.

The probability that a person with type I diabetes would have had type I diabetes (and so died a painful death before 35) if born a hundred years ago is close to one, as type I is inherited. And most food was considerably less healthy and safe then, too, only more scarce and expensive. The problem with GM and processed food is not that it is less healthy than what came before it, but considerably less healthy than what can be produced today, which is the relevant reference point.

As fhars points out, type 1 diabetes is not based on diet or lifestyle. There is no reason to think that I wouldn't be diabetic if I were born a century earlier.