Rather than reacting emotionally we have to look at the numbers to make sense of this. The overall risk to Dutch cyclists (it's on page two of the document) of a "head/brain injury" is 153 per billion kilometres ridden. That means that one such injury is one per 6.5 million kilometres ridden.
On average, every Dutch person makes a trip by bicycle 5.6 times per week. This works out as an average across the whole population of 2.5 km cycled every day. That's the highest figure for any population in the world. If we assume that people cycle every day of their lives to the age of 80, and that they cycle that 2.5 km every day of their life, they will ride a bike for a total of 73000 km during their lifetime. Divide it into 6.5 million and you find a figure that a typical Dutch cyclist can expect a "head/brain injury" once every 90 lifetimes.
Note that it doesn't say how serious the injuries have to be in order to be included. However, it does give total numbers of head/brain injuries per year as 550 + 1600 = 2150 which is more than ten times the total deaths of cyclists per year from all types of injuries. For the sake of making the maths easy, let's lazily (and very inaccurately) assume that every death when cycling is due to a head injury. We then find that the risk of death due to head or brain injury when cycling is actually around once per 900 lifetimes.
Also, note that the article points out that cycle helmets can only reduce the rate of deaths due to head injuries by 29%. So, if a helmet is worn by that typical Dutch cyclist, it will save his/her life every 3100 lifetimes or so.
Death occurs once in every lifetime. i.e. Other causes of death are more than 3100 times so significant as deaths due to cycling without a helmet and that applies even in this country where there is more cycling than in any other. It applies even if for the sake of simplifying the calculation we make the horribly inaccurate assumption that cyclists never die of any type of injury. This in a country where 93% of the population rides a bike at least once a week.
To summarize, deaths due to head injuries while cycling are not a major public health issue and should not be treated as such. Helmets are not the answer to cyclist deaths. Good infrastructure is what makes cycling safer.
A contrast with another cause of death:
A couple of days ago I saw some other statistics, about a much more common cause of death and injury. This covered the risk of car crashes to Britain's children. In this post is the alarming statistic that one in 27 children in Britain, more than one in every classroom, can be expected to be killed or injured in a road crash by the time they are 16.
Think about it. If the risk is similar in other age groups, then there is a chance of one in five that you will be injured or killed in a road crash during your lifetime. That's a risk due to motor vehicles which is many times greater than that faced by cyclists in the Netherlands not wearing a helmet.
Britain's roads are actually amongst the safest in the world, for drivers. However the risk of death or serious injury from road crashes elsewhere is higher in every other country than this one, where there are more cyclists than in any other country.
Previously I covered the efforts that car manufacturers have put in to make driving appear safe.
Also... 2.5 km per day may not sound much, but this is the highest average cycling per day per person figure for any country in the world. It's the average distance cycled for absolutely everyone, all age groups, through the entire year, averaged across an entire lifetime. By comparison, English speaking countries all hover around 0.1 km per day by bike per person (look it up if you don't believe me). In all places, keen cyclists of course cycle a lot more than the average. Long distance journeys by bike are also more common in the Netherlands than in any other country.