Given the undercurrents which motivate society, and the way in which those undercurrents and moral constraints work against Newland's own happiness, it is ironic for him to be defending the cultural milieu in which he lives.
Clothes, and colour, are a recurrent theme in the novel. There is some degree of irony in the way that Ellen's dark colouring and red dress are contrasted with May's pallor and her white gown, since in the end it is May who becomes manipulative and scheming, whereas Ellen, in her refusal to embark on a clandestine affair with Newland, displays a considerable degree of ethical standards which are not dictated by society. .
In chapter four, when Newland and May go to Mrs Mingott's, it is clear that Ellen is the one who is independent and follows her own course of action, whilst the others are concerned with unimportant details of social convention such as the layout of the house, and whether it is suitable to have the bedroom and the living room on the same floor. When Ellen suggest that Newland visits her, which in another social context would be perfectly acceptable, it is clear that in this culture, such a meeting would be unheard-of.
In chapter five, there is considerable irony in the discussion on freedom which takes place between the characters. Newland has already expressed some vague disapproval of Ellen's unconventional ways, but now he is defending her and asserting that she should be free to do as she pleases. When he states that women should be free', it is an odd remark for him to make - ironically enough, he feels that May should be allowed her freedom, and yet in the end she probably has more freedom than many of the other characters.
At the same time, it could not be asserted that Newland himself is free, since he is constrained by the dictates of society as much as any of the others.