Cereals have a high glycaemic index even without any additives, so they’re objectively not good food.
There’s food with a high glycemic index that is most certainly not “bad food” (like fruit), and there’s food with a low glycemic index that definitely could be by what I assume is your criteria (like butter).
Also the statement “cereals have a high glycemic index” isn’t even true, since some of them do (like corn flakes), while some of them don’t (oatmeal, which is close to oranges).
https://www.dietandfitnesstoday.com/glycemicIndexDetails.php...
And besides, I think we all decided that sugary soda is unhealthy. But we still consider cereal healthy. They both seem to trigger a similar metabolic response, and have a similar satiety profile.
Everyone chooses for themselves, in their own circumstances, though. Even straight up eating glucose with caffeine makes for a great pre-workout mix in a pinch.
In other words, it depends on the person. :)
Some people are not fans of eating things approaching soda GI, as they have a feeling of a sugar rush, followed by a crash and hunger. No need for a medical condition - it can simply be a dietary preference.
It depends on the person and circumstance whether GI above 55 is high. Everyone needs to figure out for themselves, but it helps to be aware of GI in food and see how different GIs make you feel and function. And it helps to be aware that soda-type GI isn't considered very healthy by some, with ongoing debate.
Also, possibly 55+, 65+, or whatever arbitrary threshold is not too high for most people. There's some debate around that now. So I still think it doesn't hurt to be aware. But possibly.