The conclusion is simple and you might have heard it before; biking should be kept simple! No helmet, More simple!
In addition the article also shows this interesting diagram (from Trafikanalys):
It is very clear that the risk of getting killed per kilometer traveled is much higher when biking than when driving a car (4 times higher). However the risk of dying when walking is actually much higher, times higher (almost double compared to biking). Yet, no one would argue that you should wear a helmet walking. The contrast to the travel modes where helmets are currently requested by law in Sweden is stunning. It is so much more dangerous to drive a moped or motorcycle than even to walk...
However, if we look not at risk of dying by traveled kilometer but by time spent driving a car, biking or walking that kilometer we see that each of these transport modes is about equally safe while driving a motorcycle or moped is much more dangerous.