It's not the Ajax fans that are the problem. It's their hooligans. I heard reports that the rest of the stadium was cursing them for throwing flares on the pitch.
It seems to me that the Netherlands haven't managed to deal with organized hooligans so they get to act up.
This incident is giving Dutch fans massive flashbacks. In 1989, Feynoord hooligans exploded several crude homemade bombs outside Ajax’s stadium, which caused dozens of causalities. The crack down after this pushed a lot of the hooligans activity away from the stadiums and into remote, prearranged locations.
in 1997, Feynoord & Ajax hooligans met up at a spot off the highway in a town called Beverwijk. One of the combatants died, which drew renewed police and political attention to hooliganism.
The off-site rumbles continued, but for most Dutch folks it was an out of sight, out of mind problem. But things changed during the pandemic lock down. During the empty stadium phase of return, hooligan groups broke in during matches causing cancellations. Last year, Davvy Klassen got hit in the head with an object in the middle of a match; he ended up with stitches and a concussion. And then there was the insane scene of AZ hooligans trying to overrun Hammers fans last spring.
centrist and leftist parties in the NL parliament want to take bold action and have been making public pronouncements about hooliganism since the AZ/Hammers fiasco. But the right wing parties see common cause with the hooligans and have been slowing debate as they try to leverage greater restrictions on immigration and expressions of Islamic faith in public. So while the large majority of hooligans are disaffected white youth, the right are pushing for all actions to apply equally or more so to African and Muslim communities. So action has been very slow. This incident adds new urgency, though.
Edit: for the V&N nerds in the room - the Dutch lower house, which is where all the debate & law making happen, is a close 77-73 split between a centrist coalition and the range of parties on the left & right. 5 of those 77 seats are held by the Christian Union, an economically progressive & socially conservative party. They have been a stumbling block on a lot of the PM’s agenda.
And then there is the Senate, which in the Dutch system only has veto power over House legislation, no law making power itself. The coalition that controls the House actually holds a minority in the Senate, adding further challenges.
TL;DR the Dutch government is just as divided and dysfunctional as the US right now. Even an issue that is outrageous to the large majority of the population is being stymied by partisan jockeying.