Addendum:
People often underestimate just how dangerous speeding can be. Going 20km/h over the limit doesn't mean if you crash, it'll be at 20km/h higher than the limit. Because you're moving faster, even if the total stopping time would only increase by 25%, the distance covered during that stopping time would be much higher, meaning you reach the "crash" point earlier during the braking process, and at a much higher speed. That's why small changes in speed can have exponential impacts on the severety of a crash.
For a simplified hypothetical.
If two cars are driving down a road with speed limit 80km/h, one is keeping the limit, the other is going 100km/h. When they are exactly neck on neck, at a dirt road intersection ahead, a tractor driver doesn't check left and right properly, and starts turning onto the road.
Both drivers notice the tractor at the same time, react equally fast (average reaction time from recognition of a hazard to the start of brake application) and slam on their brakes as hard as they can. Using average deceleration rates for emergency stops, if they noticed the tractor early enough that the car following the speed limit just gives the it the tiniest of kisses, coming to a full stop right when reaching it, then the car going 100km/h would have crashed into the tractor whilst still going 80 km/h.
That's going from a succesful emergency stop to an almost certainly fatal accident, over "only" 20km/h speeding on a high speed road. After subtracting measurement tolerances from a speed trap, in most countries that wouldn't even get you a license suspension.