there are different types of sugars
lactose, dextrose, fructose etc

they each have different properties and yes excess amounts of each have negatives.
your body does need sugars and each type of sugar has a different effect on the body

there are simple sugars which your body just uses direct as energy which can cause excess bloodsugar if taken too excess. there are also complex sugar which take time to breakdown.
there are also sugars which take time to break down but your bodies initial reaction is to spike the insulin which can actually cause a mis match of your body slowing down due to insulin and then speeding up later due to the sugars.
its where people after a meal feel sluggish and then get a second wind later

yep it isnt the christmas turkey making you having the christmas afternoon nap. its all the carbohydrates from the potato's and gravy that triggers your insulin

short summary.
dont eat to excess and your body wont go wild trying to control the uncontrolable
so control what you eat and your body will control the rest