They wouldn't, because Holland actually has a constitution and decent self-defense laws. The most famous case I can remember, the wife of a jeweller shot a bunch of guys dead who were trying to rob their store. The families of the poor widdle criminals cried dindu nuffin but the judge ruled the case as self-defence and only gave the couple some community service because the gun was illegal.
The nigs were also from the Dutch Antilles, not African migrants. It'd be kinda hard from a legal point of view to close the border to your own citizens and a part of your own country, as much as all of us here would probably like it.