Because there have been lots if studies showing that if parents are open and honest with their children that donor that the children have if anything better relationships with their children and that the marriage tends to be stronger (not as a result of the fertility treatment IMO as it's a self-selecting group, but even so...). But no, they have to feed into the usual DM predudices about blood being thicker than water etc. etc. Not counting what that says about adoptions.
DM article here
Research for example like this:
In recent years, concerns have been raised regarding the potentially negative consequences of gamete donation for parent-child relationships. Findings are presented of a study of families with an infant conceived by gamete donation. Fifty donor insemination families and 51 egg donation families were compared with 80 natural conception families on standardized interview and questionnaire measures of the psychological well-being of the parents, the quality of parent-child relationships, and infant temperament. The differences that were identified indicated more positive parent-child relationships among the gamete donation than the natural conception parents, accompanied by greater emotional involvement with the child. Comparisons were also carried out between the donor insemination and the egg donation parents on their experiences of gamete donation. In contrast to the findings of earlier investigations, the donor insemination and egg donation parents appeared to be more open toward disclosing the donor conception to the child. It was concluded that infants conceived by egg or sperm donation did not appear to be at risk for parenting difficulties. Copyright 2004 American Psychological Association