I'm not sure there is an autism "epidemic". I suspect back in my day, folks with autism were simply not diagnosed as such.
Now, it is also possible there are some dietary influences, though "refined sugar" is really not different than "raw sugar", nearly as I can tell, other than being purified. Maybe the trace ingredients in raw sugar are somehow beneficial? I doubt it.
My problem with "sugar" is fructose, one can read about how it is metabolized, it's a bit scary. And "back in my day", a very typical breakfast was comprised of highly processed cereals and milk, like Frosted Flakes, this stuff isn't new. It's corn flakes with a lot of sugar added.