Earlier quoted context omitted.
Reducing speeds is a form of collision prevention, is it not? A typical car can just about stop on a dime at 15mph, and a pedestrian has more time to react. There's a whole slew of other pedestrian-friendly street design that we could & should adopt as well, but that doesn't make speed any less of a valid approach.
Speed, in of itself, is not dangerous. What is more dangerous on highways is differential speed. i.e. if you're driving 60 mph when the traffic around you is doing 80 mph, you're the problem. Probably exponentially so if you're driving slowly in the "fast" lane. While rarely enforced, most states in the US have laws that require you to pull to the right if you're impeding traffic (usually defined as holding up +2 veh…
That sounds like an extraordinary statement to me, by which I mean that you need to support it.
First, let me make a distinction between crashes where drivers lose control after the collision, either due to shock to the driver or damage to the car, and crashes where they don't. In the latter case, I agree with you; a freeway scrape where both cars can slow in a controlled manner is probably pretty safe. And you are more likely to have that sort of accident when you are going at similar speeds in the same direction. But it's not a certain thing;
Cars are complex systems, and designed to operate without colliding with other vehicles. Cars are also much more likely to lose control when they are operating closer to their speed design envelope.
However, in the case where either the car or the driver is incapable of continuing to control the vehicle, at that point the car continues to hit other things until it's stopped (and is often hit then by traffic that isn't stopped.) At that point, total speed matters a lot.
There is just a whole lot more energy involved when you are moving fast than when you are moving slowly, and when energy is dispersed in an uncontrolled manner near people, those people tend to get hurt.