You're just asking for ineffective labels (eg California prop 65) or corruption.

Coca-cola has 10.6g of sugar in 100ml. Apple juice has 10g of sugar. Breast milk is about 7g of sugar. Cow milk is about 5g. Coke zero has 0g of sugar. Which of these would you label as dangerous?

French fries, hamburgers, pizzas etc tend to have relatively little sugar in them. Apples have about 50x the sugar content of McDonald's French fries. They're high in carbs, but not necessarily "sugar". Will they escape the label or will they get it for general carb content?

I didn't downvote, but I think your solution isn't particularly effective. Part of the problem is food is more fundamental than tobacco; nearly everyone finds some kind of sweet treat appealing. Slapping labels on all the poptarts saying they are 'desserts' doesn't fix the fact that we are almost all hardwired to seek out fats and sugars.

We are also hard-wired to seek out salt, not to mention the energy boost and the hand occupation offered by cigarettes.

I think I agree with you in some ways. You may be being downvoted because "clearly labeled as a dessert" is too strong. Maybe we need categorization for quantity of sugar per serving, eg. 1-10g, 10-20g, 30g+ or whatever with different colors or labels. It's very easy to fall for feel-good marketing (eg. healthy/low-fat/organic or whatever) and not realize how full of sugar something is.