One: The Letter Of The Law
When the Selection Law was passed rather forcefully through the Wizengamot courts, the entire wizarding world, particularly the "old guard," of the pureblood Sacred 28 Families was beyond shocked. Each pureblood, halfblood, and deatheater had to donate, or face mandatory imprisonment in Azkaban, Nurmengard, or be killed by Minister Thicknesse's orders, the execution sentence to be determined by the Minister's pleasure.
In reality, it was Lord Voldemort who made these decisions, and every magical person had to comply...or else. The belief from the so called dark side, was that by destroying every muggle ovum and sperm produced at these banks, the muggle population would be flooded with magical pregnancies within the fullness of time.
But as our story begins, we open up on to a lonely muggle lady who was just trying to get pregnant, and got more than she bargained for as a result....