Saying that food with a high glycemic index is simply “not good food” shows a lack of understanding regarding what the glycemic index indicates and what constitutes “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).