Macmillan was one of the first people to articulate a vision of South African as a single society. This view brought him into conflict with the segregationist government of the day as well as with liberal segregationists. He became chairman of the Johannesburg Joint Council of Europeans and Natives and was involved in 1932 with public clashes with the ministers of Native Affairs and of Justice – the latter was Oswald Pirow. After the University of Witwatersrand sought to gag Macmillan, he went on sabbatical leave at the end of 1932, but he did not return to the university. He resigned in September 1933.