Pro: Responsibilities should be assigned to those individuals who have control over the cause of significant events. The use of semen to procreate human life is a significant event. The sperm is the direct cause of the fertilization of the egg. The semen donor is fully aware that his sperm is used to create new human life. No one bears more responsibility for the use of his semen than the semen donor.
Con: The sperm donor is not responsible for how other parties use his sperm. He is typically anonymous and has no part in the decision regarding which female is inseminated.
Few people care about their bloodlines or root their self-concepts in their lineage. And with the increased use of reproductive technologies, the concern for knowing one's own ancestry may recede further. As technology becomes increasingly capable of manipulating the genetic makeup of human beings, the genetic contributions of individual parents will become less important to the children and to the society in which they live.
For genetic contributions will be understood to be as random as the directions of leaves in an autumn wind. Whether the names of two people the union of whose gametes produced a given individual are known or not, those who nurture a child and help to bring it to maturity—the social father and mother—create the strongest bond with the child, have the greatest influence on the child's character and on the direction of the child's life, and are therefore likely to garner the most affection from the child.