I dont want to get into the merits of the quote, but here is the original, and it wasnt said by keynes.:

But by far the strongest resistance to drastic action comes from those who would say, if they sought at all to express their motives, that inequality of incomes is inevitable and even desirable in a world in which individuals are born with unequal talents. You must leave the efficient man as well as the inefficient the motive to exert himself to the utmost. The great merit of the capitalist system, it has been said, is that it succeeds in using the nastiest motives of nasty people for the ultimate benefit of society

https://quoteinvestigator.com/2011/02/23/capitalism-motives/