History is to blame
Haines' guilt about the Irish history that Stephen experiences as a nightmare, and that his own nightmare perhaps has something to do with, comes out of his mouth reeking of British imperial euphemism (“We feel in England that we have treated you rather unfairly”) and evasion of responsibility (“It seems history is to blame”). But at least he does feel guilt.
It is easy to scorn Haines' manner, and Joyce doubtless intends for his reader to do so. In Scylla and Charybdis Stephen thinks of him as a "Penitent thief." But Stephen’s prickly resentment does not necessarily appear to much better advantage than Haines’ suave unconsciousness, and as he smokes Haines' tobacco he reflects "that the cold gaze which had measured him was not all unkind."
If Haines is like Trench, his English family is descended from members of the Anglo-Irish Ascendancy, and he is returning to the land of his ancestors not simply as a tourist (though he certainly is that), but as an expatriate motivated by nostalgia and admiration for Irish traditions. His admission that England has treated Ireland unfairly aligns him with the Liberal politicians who worked to atone for past injustices in various 19th century British Parliaments. In the last few decades of the century this liberal guilt produced some incremental land reform in Ireland, and it very nearly produced Home Rule under the leadership of Prime Minister William Ewart Gladstone, who makes an appearance in Circe as "Grave Gladstone."