Being familiar with (some of) the scientific literature, it’s almost surely not something “simple” causing obesity. It’s a complex, multifaceted problem, and even though I too am a sugar hater, implicating it directly as the addictive caloric poison drug isn’t even close to a complete answer. I am probably simplifying this too much, but the added sugar phenomenon seems to have spawned from removal of fats, which itself proliferated from some bad science originating in the 1950s.
I’m doing this from memory and taking liberties here, but in other words it was this plausible-sounding “fat makes you fat” theory that was being pushed by the medical community and scientists with lots of scary info about heart disease (based on spurious correlations). The government eventually endorsed this in the late 70’s with the dietary guidelines and then other dumb shit like the food pyramid, and, well, people take note of this and adjust their diets accordingly. It’s why my mom still thinks fat makes you fat despite me explaining the calorie model to her repeatedly. Like, if you start with a really flawed and entrenched understanding of how something works, it’s confusing when you attempt to rectify statements that don’t fit that model. Example:
Belief: Dietary fat is the main driver of obesity.
Mechanism: Fat is a molecule and when you eat it, it goes directly into your arteries and fat cells where it’s stored until you burn it off by presumably doing a bunch of cardiovascular exercise.
Claim: “You are all complete fucking boors for putting sugar-loaded fake butter on your filet mignon instead of real butter.”
It’s really tough for someone to make sense of this claim if their model of the nutrition universe revolves around the dietary fat == fat identity and god knows how many other ridiculous misconceptions like magical properties of ill-defined “healthy” foods. You have to know stuff about calorie balance, satiety, insulin response, etc. for it to really make sense. I think you’d be surprised at how many people I know doing FOOD RESEARCH don’t know this shit.
And the reason a calorie density tax isn’t great is because it ignores things like satiety. I just had ice cream from a local place that I can manage about one scoop of before tapping out. It’s incredibly rich, sweet, and filling. Like, however many calories it was in that tiny cup, my body said stop now. The same isn’t true for, say, pizza, which I seem to be able to binge until full stomach capacity and may still find myself wanting more even if stuffed.