Sweet is not harmful in itself; harmful are refined carbohydrates - like sugar. So, fruits, dates, sweet potatoes (yam) and other sweet whole plant foods are healthy, but sugar, white bread (made from refined cereals), fruit juice, isolated starch are harmful.
So, if talking about the optimal for health, the amount of refined carbohydrates consumed is zero. Our physiology is not adapted to this invention of modern civilization, existing only for a moment on the scale of human biological evolution.
The problem is the speed of assimilation. In their natural form - that is, inside whole plant foods like fruits or cereals - sugars and carbohydrates are absorbed slowly when we consume them. Thanks to fiber and other phytoelements that slow down absorption. But refined carbohydrates are absorbed too quickly! We do not have time to effectively distribute them throughout the body. An imbalance is created. Consequences?
Everything is very individual. For example, throughout my life I eat not just a lot, but a lot of sweets - I put 5 teaspoons of sugar on a 0.3 liter cup of tea, I always drink tea with jam, honey, sweets, sometimes also with cookies / cakes ... I drink tea two or three times a day. At the same time, I have neither diabetes nor excess weight. And one of my brothers does not eat sugar or sugar-containing foods at all. However, he is overweight. Therefore, there simply cannot be general recommendations.
There are no universal nutritional standards, it all depends on the individual, his goals (for example, the desire to lose weight / gain weight), the level of physical activity, age, weight, gender. On this issue, you can consult with a therapist or nutritionist.