Actually, it is a more for safety purpose as in France at least, the number of people wounded when they transport an unprotected knife of cutting object is much higher than the number of people wounded in a fight.
I have practiced fencing for more than 20 years and all the wounds heavier than a little blood on the nose or finger I saw were due to improper or stupid manipulation of the weapons, never during a "fight".
Still, the police have a legal motivation (especially because actually the law saying something like "proper safe packaging" is a little vague) to confiscate them in case of risk of streetfight or similar situation and as such it is very usefull.
There is basically 1/3 chance that this law would have avoided such drama.