He may not know all the arguments in favor of the apartheid, but he knows that the issue has been examined over the decades in various cultures and the expert opinion is against it.
For a thousand years and more, you could say that about the existence of God.
If that's the only question these heuristics and arguments get wrong, I'd say that's pretty darn effective heuristics and perhaps I should base everything I believe on what they say.
Related: Heuristics for Evaluating the Soundness of the Academic Mainstream, Admitting to Bias, The Ideological Turing Test