In the U.S., a fertility clinic may use a single donor's sperm to fertilize a large number of eggs in vitro:
Today there are 150 children, all conceived with sperm from one donor, in this group of half siblings, and more are on the way.Mel Brooks, please make a new movie, "High Motility." Yet another chance to use the line, "Great knockers." (Yes, I know that was in "Frankenstein.")
Imagine, though, the strange inner life of the donor. He's as reproductively fit as kings and khans of old - with no commitment beyond, presumably, pornography. Does the clinic call him and plead for more whenever they have a tough case of infertility?
There's a product here, there's unrestricted economic activity, many people are happy. But... there is no conceivable and credible just-so story by which the free market can definitively solve the problem of potential incest. A free market requires full information, exactly what is not available in this market for semen.
Regulate or risk half-sisters marrying half-brothers?