It kills by causing serious collisions before you can do anything about it. You can't control a car if you don't have time.
Few people are aware of the extent to which speed increases risk of serious accident. Most people know stopping distance increases with the square of the speed (stopping distance increases 21% when speed increases 10%; stopping distance at 35 mph is 96% greater than at 25 mph). They do not quite understand that means the risk of any accident also increases with the square of the speed. Control is lost by running out of time.
It gets much worse. Impact forces, and the severity of the impact, increases with the fourth power of the speed. If you strike an object (like a human) at 35 mph the severity is nearly 4 times that at 25 mph.
When you combine the two, the risk of an accident of any given severity (like crippling or fatal) increases by the sixth power of the speed: at 35 mph you have 7.5 times the risk of a crippling or fatal accident as you do at 25 mph.
How can it get worse? There is a point at which all is lost. For similar vehicles, when the collision speed, head on, reaches 71 mph survival is a fluke. At 65 mph the risk of death is only 70% and at 61 mph, just 10 mph slower than the 71 mph extinction point, you only have a 54% risk of death in the same collision. Combine the square of the speed for risk of collision (the loss of control you talk about - no time to prevent it) and the cost of speed is outrageous.