It kills innocent people? You sure that's the reason? Drug laws kill innocent people: 8 out of every drug related death is an innocent, yet we still have drug laws.
And how do you assess "speeding"? If we all drive at 5mph there would be no road deaths. None. So whats your point? If granddad is ok to drive at 55 in his '75 buick with bouncing suspension, then I'm ok to do 90 thanks: including reaction time, I can stop in the same distance.
Speed limits were introduced to save GAS not LIVES. Now they are there to save money.
Around schools and through residential areas, 5mph should be the limit if you want to save lives. You up for that?