Instead of focusing on saying “this is wrong,” try to add new information that is related to the discussion and that could stimulate readers’ minds
That allows the trolls to control the direction of the discussion by picking a topic and having other people add new information to it. Some topics are inherently inflammatory or inherently are likely to attract people who behave badly, so even letting the troll pick the topic can be a disaster. You do not want to have a troll arguing that Jews descend from Cthulu, provide “new information”, and attract people sincerely arguing that Jews are not descendants of Cthulhu but are as evil as if they were, or even just Holocaust deniers.
That allows the trolls to control the direction of the discussion by picking a topic and having other people add new information to it. Some topics are inherently inflammatory or inherently are likely to attract people who behave badly, so even letting the troll pick the topic can be a disaster. You do not want to have a troll arguing that Jews descend from Cthulu, provide “new information”, and attract people sincerely arguing that Jews are not descendants of Cthulhu but are as evil as if they were, or even just Holocaust deniers.
You can’t reduce anti-Semitism without first attracting anti-Semites.