Sugar is a double-edged sword. My philosophy is "everything in moderation". Luckily, I don't need to watch my weight, and I never feel guilty for eating a sweet treat. Fizzy drinks are not only bad because of sugar. There's so much other crap in there, the sugar would probably be the least of my worries.
When you compare to the low sugar intake by ancient humans, have you come across articles talking about use of the brain? As far as I know, the brain is a sugar-dependent organ. It's the last one to switch to ketone metabolism in times of starvation. Do our modern lifestyle and work activities not require more brain activity, which might contribute to making our body crave sugar?