I'm not sure what the 0th law should be, but we have to have one.
Anyway, I think this view is a little simplistic. We have many laws in England, but they essentially come down to just one - 1. Do no harm to your neighbour or his property. The Bible has many laws, but according to Jesus, these can be summed up in 2 - Love God completely, and Love your neighbour as much as you love yourself. The point is that these general rules describe the end result, but don't help you with the process that you need to achieve that end result. In order to enable people to keep the important rules, we generally legislate sensible processes as well. Processes like the rules of the road.
Can you, by driving safely guarantee that you will never hit another road user? No matter what you think your driving skill level is, there are always unexpected events and unforeseen hazards that can ruin your plans.
How many people have to be inconvenienced or have their freedom of movement severely limited, before you say this is a bigger tragedy than a fatality? This isn't a fair question of course, but people need to know that by driving rather than walking or taking public transport they are accepting that there is a small but real risk they may kill someone (even the good drivers). If they aren't comfortable with that risk, they shouldn't drive.
On average more than 9 people die and 90 people are seriously injured every day in road accidents. 3 of those deaths will have been because of excessive or inappropriate speed. Although most driving is motorway driving, it accounts for less than 10% of fatalities.
By far the majority of drivers think of themselves as much better than the average driver, which strongly indicates that most people have an unrealistic view of their driving skill. Studies show that people do not understand the reasons for speed limits, they are often unaware of the hazards that they speed past. My point here is that if people are told to go as fast as they think safe, almost all of them will go faster than is safe.
Anyway, it turns out that the government is trying to do a large number of things to improve safety on the roads and increasing the number of speedlimited areas is only a small part of their plan. Check out Tomorrow's roads: safer for everyone by The Department for Transport for more information. By pages, speed limits are about a fifth of their strategy (the rest being: higher testing standards, better infrastructure, education and enforcement of tiredness and drug related driving, increasing vehicle safety standards), and since excessive speed deaths are about a third of the fatalities, I wouldn't say that that is an overemphasis.
I'm not entirely sure we've got the balance right when it comes to peoples right to have cars versus environmental and safety issues, but if society has decided as it has then I think the government is doing roughly the right thing in being stricter on speed limits in the kinds of areas where most accidents occur. Since motorways are relatively safe, I think it'd be sensible to remove the speed limit on the safer stretches of motorway as they do in parts of Germany.
I can only really think of one way they could improve safety that they don't mention much in the report, and that is to encourage the police to use careless and dangerous driving charges more often. This would mean people might be charged for breaking the 2 second rule etc, but it would lead to very subjective policing. At least now, even if you think it's an ass, you know if you're breaking the law or not.