The sibling comment answered perfectly, but I'll add that your advice sounds reasonable in a vacuum, but in reality this event happened one year after the start of genocide. The community had no reason to believe that the state would do anything, as the state allowed a genocidal country's genocide-celebrating citizens to travel to the community's city for a football match and the police didn't do anything while they were chanting death to arabs, hours before the locals took matters into their own hands.

After a year of international inaction in response to the genocide, the Amsterdam community acted quite reasonably, and to be honest quite commendably, by stomping the lynch mob into the gutter, as the sibling eloquently put.