This is an unfair premise because it implies that breaking the speed limit is always unsafe. This is flat out not true; millions of drivers break the speed limit every day and have never or will never face the consequences. Out of various dangerous acts, speeding certainly counts as one, but it is not as fatal as, say, playing with firearms.
There are plenty of valid reasons to speed:
* (Most common) The actual speed limit is way too slow for what the road conditions are, and everyone would suffer if they followed it
* You are trying to overtake a truck and avoid their blind spot (I have done this; the less time spent next to a truck, the less anxiety you feel)
* An emergency vehicle is behind you and you need to speed up to overtake a car in the other lane so you can lane-change and make way for the vehicle (State v. Brown)
* Everyone around you is speeding; going slower is more dangerous because people need to lane change to get around you
* You are trying to make some space between some kind of maniac driver who you believe will soon lose control and hit you (I have done this to get away from drunk drivers)
* Your loved one is experiencing a medical emergency and you need to get to the hospital
* You are being chased by some kind of criminal or terrorist
* You are avoiding a natural disaster such as a rockslide, tornado, flood, or avalanche
Realistically, will you ever be driving away from a rockslide or sedan terrorist? Probably not, but with a regular car, you at least have options to exercise if you ever are in that spot; with a limiter those opportunities are gone.
In the case of a limiter, a mis-configured or broken speedometer or sensor can give false readings that severely inhibit your driving, even while driving, which could cause an accident if your vehicle slams the brakes without warning. It could also prevent you from using highways if your vehicle is not capable of accelerating past 40mph. This is the same argument against self driving cars; humans want control to keep themselves safe, not so they can be dangerous.
But would you buy a car that hits the brakes at the speed limit? Not an alert. An actual limiter that you cannot bypass.