Sugar is sugar. Too much is bad for the body.

Fruit has fiber. Fiber makes your body use up the sugar slower.

Chocolate and desserts don't have the fiber that slows it down so it uses it quickly.

When your body uses sugar in a quick way like when you eat chocolate, it spikes like you're going up a really high rollercoaster. When the rollercoaster has to come down from the peak, you will feel bad but feel like you want to go on the rollercoaster again.

If you keep riding the rollercoaster over and over again, your body will eventually not be able to keep up and you will end up with insulin resistance or diabetes. This means your body can't send the right signals to use the sugar in an efficient way anymore.