As I delved into it, the whole issue of the relationship between speed and accidents is actually very interesting. Research conducted by the Florida Department of Transportation showed that the percentage of accidents actually caused by speeding is very low, 2.2 percent, and a large proportion of this related to speeding on rural roads not major highways. In fact, research has overwhelmingly and consistently shown that those driving 10 mph slower than the prevailing speed limit are far more likely to cause an accident than those who exceed the speed limit by 10 or more MPH. So it actually looks like those who fornicate the canine are far more dangerous than those who speed.
It also occurred to me that the reality in Canada is far different than in the US. In Ontario, for example, the posted speed limit on major highways is 100 km/h (about 60 mph), materially less than the prevailing 70 mph (or higher) in most US states. In Ontario though everyone who lives here knows that the "real" speed limit is far higher, and virtually everyone in the know travels 120 kmh-130kmh on the highways and expects that everyone else will do the same. It has been suggested that this leads to a culture where speeding is not only expected, but effectively required. There is a movement to increase posted speed limits here to accord with the real world.
Those who oppose increasing the posted speed limits here point to the higher limits in the US and the fact that the US, per capita, has a far higher traffic fatality outcome than Canada and they blame, without evidence, the higher prevailing speed limits in the US as the cause.
All of which is to say, it is a complicated question with a complicated answer. Clearly as a society we are prepared to tolerate, from a cost/benefit perspective, a certain number of fatalities so that we aren't inconvenienced in our travel. For example, we could drastically reduce the number of traffic fatalities if we reduced the speed limit to some absurdly low number and incurred the cost of a massive escalation in enforcement relating to both speeding and other "bad driver" behaviour. This would clearly reduce fatalities, but we aren't prepared to incur the inconvenience (i.e. the cost) in order to achieve this positive outcome.