Da was a big bigot. I wonder how much Wil's father impacted upon him. The whole idea for the son to rebel against his patriarch is a strong one. Ireland is entirely based around patriarchy which has enormous bearing on families, especially on sons. Another idea well presented in The Rainbow Singer is the alienation, which can befall young men from the mere presence of teenage angst.
Men do find it more difficult to deal with the past.
Men don't tend to analyse as much as women, which means when something life-changing does occur they are more likely to be less equipped than women to deal with it. This is perhaps what happens to Wil. He is unable to cope with the rejection of Teresa. Any other young man, however, would probably not have gone to the extremes that Wil feels capable of doing because he has been brought up in a society where violence is normalised to a greater extent. The novel is also a comment on American society where relaxed gun laws and their gung-ho mentality have sometimes impacted disastrously.