I would have thought that if they are off by default it would be easy to miss turning an activated one on. The present system is more fail safe. In the UK we have a program called SPINE, with this you download all the active NOTAMS for the day, having reviewed them and deleted those of no interest. I certainly wouldn't want them to be off by default, because any that show, are active and needed.
There are at least 44 NOTAM activated areas in the Netherlands and they all have to be checked and disabled one by one. Maybe 10 are activated per day, so it is a lot easier to activate only these 10 then to disable 34.
An ON/OFF switch would then be the best solution (with the possibility to turn the areas ON seperately). Anyone can then decide for themselves what is shown.