Why aren't ALL cars fitted with speed limiters?

Most countries have national speed limits on roads; 70mph in Britain, 60mph in most of the US, 130kph(about 80mph) in much of Europe. Most cars on sale will do over 100mph (160kph) and many will do much more. Why? If ALL cars (except perhaps police cars) were fitted with speed limiters we'd reduce accidents, save fuel, save on police time, save the cost of many speed cameras, save on warning signs, stop accidents where kids steal a car and 'see how fast it'll go'. Can anyone think of any reason why we shouldn't fit every vehicle with a speed limiter?