Refer them back to the research study done in Sweden (I think) that found out that it is the father who determines the child's moral compass. Mothers can nurture and love, but it's the father who sets the principles by which we live. Think about how many people you know who turned out bad because of lack of father participation in their lives and how many you know who turned out well who had good fathers. My experience with people has convinced me that the study is dead on right.
See, it's items like that that make me thank God my mother found a good man to be my stepfather. The odds were certainly against her (and me and my sister), but my stepfather has been the best daddy a girl could ever want.
(Which is probably why at 36, I'm still my daddy's girl.)