It's hard to have a serious accident when you're going under 10 miles an hour. And I also disagree that blunt knives are more dangerous. One might give their child a plastic knife which is totally blunt, but not a super sharp machete.
A plastic knife is barely a knife at all, it's almost completely useless and so is a 10mph road.
The solution to road safety can't be to drive at jogging pace. Roads are still a transport infrastructure and for practical reasons, speed has to remain an evaluation metric (a good road is both safe and fast). There's plenty of examples of safe and performant roads. We wouldn't want to make the 50 mile commute to the shops or work over the course of several days.