Like everyone else I'm for herd immunity, and like some people I believe the Holocaust of six million Jews was a sad and real historical event and that Al-Qaeda organised the September-11 attacks. But when it's appropriate to respond to Holocaust deniers or such like, we should do so with reasoning, not ad hominem attacks. John Dickson linked to this article by Philosopher Patrick Stokes; which was meant to argue that people who have opinions should defend them with arguments. However what Stokes really does is argue for "All animals are equal, but some animals are more equal than others." He says as much here: "And this attitude feeds, I suggest, into the false equivalence between experts and non-experts that is an increasingly pernicious feature of our public discourse." No Stokes, amateurs and experts alike can weigh up the validity of arguments.