Fruits contain some natural sugar and although too much sugar has been said to be bad for your health it's not really the sugar contained in fruit that is harmful for your health unless you consume way too much of the fruit.
The sugar that is bad for your health when eaten too much really comes in the bags of sugar or fructose that is not natural.
It would be impossible to eat enough fruits to cause any harm to your health from the sugar content although the sugar contained in fruit could cause you to gain more weight if you eat the fruit in excess.
But you should still eat a healthy amount of fruits to get the Vitamins and nutrients to keep your body healthy and boost your immune system.