Is there much difference between sugar and refined carbs like white bread?
https://www.nature.com/articles/nn.4224
This is important because eating when you're not hungry is a huge risk factor for obesity. It's not rewarding or fun to eat bland foods when you're not hungry, but it is still fun to eat candy when you're not hungry. This can be particularly problematic when sugary foods become a form of hedonic substitution or a coping strategy in bored or depressed individuals. Additionally, there are some studies which suggest that the tongue may become desensitized to sweetness when habitually eating sugary foods, potentially motivating individuals to choose sweeter foods at meal times:
https://onlinelibrary.wiley.com/doi/abs/10.1111/ejn.13149
White bread isn't good for you, but it lacks these effects.
I think people are talking about adding sugar for taste, beyond what the yeast can metabolise, which is common in US food culture but not generally elsewhere.
I think you'll find a bowl of oatmeal hard to beat for satiety, and that's super high in carbohydrates (~70% carbs). Compare that to a glazed donut, which has fewer carbs and more fat, and I think you'll find that the oatmeal is more satisfying.
I think most diets ignore perhaps the most important part of successfully losing weight: feeling reasonably full. IMO, the macros don't matter nearly as much as the satiety of the food you eat, since feeling full is a huge help when trying to avoid excess calories.
Not all white bread is identical either. Sugar content may vary a lot from brand to brand. Glycemic index too.
Fructose gets processed in the liver whereas glucose goes into the blood stream triggering insulin response.
Other very fine points are glycemic index, for example a low glycemic index food breakdown to glucose, bypassing the liver, but is absorbed into the bloodstream relatively slowly for glucose and minimizes the insulin spike/response promoting more stable blood sugar levels.