This passage from Gauri Viswanathan, The Masks of Conquest, I think is as brief a explanation as is possible of what allows people as varied as Niall Ferguson and Zareer Masani to claim that the British did some good in India, and for a lot of smart people to buy into it. This is what the whole Macaulay episode is about; it is a key event "in the progressive refinement of the rapacious, exploitative and ruthless actor of history into the reflective subject of literature". We are asked to look at what the English colonialist professed, most significantly through his literature, and not at how he actually behaved.
The affirmation of an ideal self and an ideal political state through a specific national literature—English literature—is in essence an affirmation of English identity. But that identity is equally split along the lines of actual and ideal selves, and the Englishman actively participating in the cruder realities of conquest, commercial aggrandizement, and disciplinary management of natives blends into the rarefied, more exalted image of the Englishman as producer of the knowledge that empowers him to conquer, appropriate, and manage in the first place.
The self-presentation of the Englishman to native Indians through the products of his mental labor removes him from the place of ongoing colonialist activity—of commercial operations, military expansion, and administration of territories—and deactualizes and diffuses his material reality in the process. In a parodic reworking of the Cartesian axiom, the Englishman's true essence is defined by the thought he produces, overriding all other aspects of his identity—his personality, actions and behavior. His material reality as subjugator and alien ruler is dissolved in his mental output; the blurring of the man and his works effectively removes him from history.
The introduction of English literature marks the effacement of a sordid history of colonial expropriation, material exploitation, and class and race oppression behind European world dominance. The English literary text, functioning as a surrogate Englishman in his highest and most perfect state, becomes a mask for economic exploitation, so successfully camouflaging the material activities of the colonizer that one unusually self-conscious British colonial official, Charles Trevelyan, was prompted to remark, "[The Indians] daily converse with the best and wisest Englishmen through the medium of their works, and form ideas, perhaps higher ideas of our nation that if their intercourse with it were of a more personal kind."
The split between the material and the cultural practices of colonialism is nowhere sharper than in the progressive refinement of the rapacious, exploitative and ruthless actor of history into the reflective subject of literature.