I'd bet a dollar per gram additive sugar tax in excess of 5g would immediately flatten the chronic disease curve. Maybe double that if it's marketed towards kids. There are a lot of problems besides sugar/HFCS but it's easily towards the top of the list.
It doesn't, it doesn't even discourage the purchases unless (perhaps?) universally adopted: Boulder, CO has had a sugar tax for a while now, and all it does is punish not curtail the consumer: often the poorer ones most as it accounts for a larger part of their income/wages. If they are so motivated they continue to buy said sugary drink at an inflated price with no benefit, or simply go 6 miles out of town and purchase in bulk if they are committed to said behaviour. I've seen it all too often,and have even managed to 'hack' the system by buying things that contain sugar but somehow flew under the radar (San Peligrino fruit flavored sodas).
It's all just window dressing and shows just how poorly educated the average consumer is in measuring the necessary caloric intake relative to their lifestyle(s), but perhaps more importantly how food has been weaponized, mainly in the US, which has a direct correlation to type 2 diabetes being so prevalent in the first place.
It's hard to blame either or entirely, but I'd saw its a 30:70 with the former and latter respectively.
The truth is I stopped drinking soda after peaking in my early 20s to late teens, I still have a relatively fast metabolism and an active lifestyle to supplement it, but the feeling you get from the sugar high of continued use has gone from energizing back then to feeling ill for hours now.
I occasionally drink soda with specific meals, often for nostalgia to this day, but its hardly a daily or even weekly thing for me anymore.
Ultimately, if your reasoning/logic were true we would see a dramatic drop in fast food consumption due to the higher prices but that simply isn't the case and corps in the fast food industry are reporting record profits YoY in this market despite the increase in price.
I see food the same way I see drugs at this point, both in excess or when misused can be incredibly dangerous, the best a Society can do is to safely regulate and educate it's populace in the pros/cons usage of both: nothing will stop a person from seeking or abusing either if they so desire. And its is a larger loss in agency for said Society to pretend it can as it often leads to draconian measures with no meaningful or effective outcome (eg sugar tax).
In fact having worked in all aspects of the food industry from farm to table for a significant portion of my life, restaurant culture and the art of cuisine/gastronomy wouldn't even be a thing if it weren't for the debauchery and the unruly excess of the clientele who were ready and willing to drop up to a day's wage on a meal(s) and accompanying alcohol were it not for the 'uninhibited decadence'a of the consumer.