... because sugar is extremely cheap. Even if it was legal, cocaine would be impossible to get that cheap, unless some DNA editing is done to make yeast shit it out maybe. If sugar cost $100/gram I could see crime happening to be able to taste some candy or non-sour bread.
The cheapness is due to the prevalence, and the prevalence of sugar caused sweetness receptors to be evolutionarily advantageous. There is no world in which sugar is extremely expensive, markets still function basically in the way they do now and humans experience the sensation of sweetness the way they typically do now. Cocaine and other types of "hard" drugs are qualitatively different in that regard.
Your example also doesn't really hold up because people typically don't process cocaine in the way they do with sugar and other carbohydrates. In your hypothetical scenario, we might see people consuming large amounts of pure sugar (or artificial sweeteners), but they wouldn't go to lengths of baking bread using it.
> Even if it was legal, cocaine would be impossible to get that cheap, unless some DNA editing is done to make yeast shit it out maybe.
Not as cheap as sugar, but probably as cheap as coffee. Coca and coffee grow in the same climates, and in recent years the cartels have bred varieties of coca that grow outside of the traditional climate as well. Imagine what modern agribusiness would be capable of.
Back when sugar first appeared in Europe, it was only affordable to upper-middle classes and above. And yet, I haven't heard about any addicts robbing people so that they can afford sugar. I don't think it's holding quite the same grasp on people as some narcotics do.