Extremists at the University of Cape Town last week petrol-bombed the vice-chancellor's office and a university bus, incited violence against white students through the use of racist graffiti, and looted and burned ''colonial'' artworks, including paintings by a celebrated black artist.Since then the country has witnessed sickening scenes of racial violence and incitement at the University of Pretoria during protests against the university's language policy, and at the University of the Free State following the disruption of a rugby match.In sharp contrast to the broadly based Fees Must Fall movement, whose largely peaceful and disciplined demonstrations last year effectively highlighted the plight of students from poor black families, hardliners from both sides appear to have taken over this time around.At the University of Pretoria the EFF and AfriForum appeared to be the major protagonists, and footage of some of the incidents suggests that some of the perpetrators are not even students.Though university managements and student representative councils have condemned the mayhem, far more effective leadership is required to bring an end to it.Thugs who assault security officers with rocks, and rugby spectators who beat and kick demonstrators, need to be identified, arrested and prosecuted.Clearly, security arrangements on some of the campuses leave a lot to be desired.It beggars belief that large groups of people who are obviously not students are allowed onto campuses to foment mayhem.University managers and student leaders need to restore calm urgently and engage in dialogue to promote mutual tolerance.If decisive action is not taken, thugs from across the racial and political divide will continue to have a field day.A fire has been started on our campuses - effective action must be taken now to extinguish it...