Sugar can be really dangerous and harmful to our health. There are a lots of reasons why and here are just a few of them :
1) Over consumption of sugar can contribute to the development of obesity and even raise the risk of heart diseases. There is also an increased risk of dying through diminished brain and physical activities, (for which I will set you the task of looking up the disease names since you introduced the idea! 😁 ).
2) Sugar influences our taste receptors. Since sugar has a very strong taste, after eating too much of it, less strongly-flavoured foods can 'seem' even less flavoursome: It can overpower the taste receptors and lead us to to feel that foods without sugar are bland.
3) Sugar and some types of drugs activate the same parts of brain, releasing chemicals that give us feelings of euphoria. Since euphoria is so wonderful for us to experience, this means that we can become very addicted to the feelings which sugar causes to be released in our brains.
After one sweet you'll often desire more and more and more. It can be is hard to stop. Similarly, sugar in our diet generally can be difficult to reduce which leads to some of the problems I have mentioned.