He takes as his theme the way in which in today's world to be prejudiced in any way, or indeed to show discrimination has moved from being the epitome of civilisation to being nigh on the nadir of existence. This he firmly rejects.
To be prejudiced is to have a preformed idea of the good, to lack prejudice is today the greatest moral attainment, but he shows how not only is it impossible, but at a deeper level utterly wrong.
The mores of today's western society he asserts are largely a result of the writings of John Stuart Mill. If, "all Western philosophy... is "footnotes to Plato"; all Western social policy is footnotes to Mill".
Mills writings have become through his later interpreters an encompassing get out clause. He rejects all authority and the wisdom of others experience in favour of a tabla rasa.
Which is of course reasonable in a meaningless fashion. But as Dalrymple points out this means that stating something uncontroversial, his example is that that the Pacific ocean is not made of melted brie, would become impossible unless one was knee deep in the brine.
"According to Mill, no question, moral or empirical, is ever settled beyond doubt, and therefore our answers to questions moral and empirical must be forever temporary and susceptible to revision... This presents him with a utilitarian argument for never suppressing opinion: if you suppress the false, you will never reach the true, and if you never reach the true, progress would be impossible".
Written with his customary clarity of thought and marshalling a heavy barrage of language his thoughts are compelling and persuasive. An attack on the desirability of equality of both outcome, and more contentious the concept of equality of opportunity as "inherently totalitarian" has undermined my own prejudice in its favour. the more As he points out, though some prejudices are wrong, that is no reason to assume that they all are.