Sebastian Dangerfield is in no way purported to be a model human being. Donleavy puts all of Sebastian's flaws out in the open: Sebastian is a vulgar, abusive, and irresponsible alcoholic. Sebastian is in no way the gallant, classic, and Victorian hero of the past. He is instead the rejection of all that was pure and virginal in previous works of literature. He is the product of Modernism.
Modernism as part of its very foundation sought to shock people. I think of Sebastian Dangerfield as a literary equivalent of the shock-rocker Marilyn Manson. Will reading how Sebastian hits his wife make readers hit their spouse? Will listening to Marilyn Manson turn people into gothic murderers? Everyone has their own opinion as answer to those questions but it seems obvious to me that readers (and music listeners) need to realize that human beings are not the sugar coated ladies and gentlemen of yore. People do some terrible things. Everyone has a dark side, no matter how slight. I was not at all offended by The Ginger Man. Perhaps it was the fact that I was introduced to the text in the anything-goes Modernist context, perhaps I am a little too liberal. I will always find this book uproariously funny though. I can always side with a character that can make commentary on the human condition without doting clichés. I can at once laugh at Sebastian and be amused by him, without being "on his side" - his very dark side.