I also tried high-fat diets that were low-sugar, because it’s very hard to escape the anti-sugar noise in our culture, even though the research seems inconclusive. In the world of nutrition (mainstream and otherwise), our puritan sense of morality is surprisingly tenacious. Anything that tastes so good, that is so seductive and desirable, and that is enjoyed so abundantly by poor people, MUST be immoral and unhealthy.
Yet even the anti-sugar people will find a way to sneak in the sugar, because sugar is awesome. I’ve seen a meme on facebook for a “sugar-free” cookie that includes raisins, bananas, and dates. People engage in all kinds of magical thinking about fruit, as if it’s anything but sugar with a “bit” of fiber and vitamins. The juicing movement is even more hysterical. They drinks tons of sugar water in the form of fresh juice, but condemn coca cola as a kind of poison. Their sugar water really is good for their health and energy levels, and in some cases helps reverse disease, but they dress up their sugar with nice stories (and pay ten times more) so they can still feel like they’re “better” than those miserable soda addicts.
You’re right that sucrose and HFCS aren’t exactly the same, but the difference seems trivial to me. If anything, the unbound glucose and fructose in HFCS make it more similar to honey and fruit juices, so the health food movement should prefer it. I’ve heard some truly ridiculous claims made about HFCS, the worst of which is that it contains 5x the calories of sucrose (in a secret form of occult, indigestible starch). This claim can be immediately dismissed by even the slightest modicum of critical thinking, and anyone could test its veracity using nothing but a saucepan and a kitchen burner. I feel like most discussions of HFCS often devolve to these kind of irrational explanations, when the real objection to HFCS is emotional. However, if you’re aware of more substantive arguments against HFCS, I would be happy to discuss them.
I used to try to eat oatmeal plain (or just with a little sugar and butter), and it would always make me feel bloated and sick. But just like you said, add tons of fat, sugar, and salt, and suddenly you have some delicious cookies.