Ok. So we have two basic arguments.
1) That increased speed = increased stopping distance and less time to react.
2) That one can hypothetically drive above the speed limit, and still be safe.
On their face, those two arguments are not mutually exclusive. I personally would worry less about an attentive, high-skilled speedster, than a distracted driver driving the speed limit.
So, here's what we do: We have monitors in all cars to record their speed. We increase the repercussions for at-fault accidents, and if speed was a factor in an at-fault accident, we punish the driver severely, even if there is only property damage.
The other side, is more stringent skill requirements, ala Germany, where fatalities are a smaller percentage than here.