My mouth is still open after learning from ABC News ("When is a Sperm Donor a Dad?", http://abcnews.go.com/GMA/Parenting) that written contracts absolving sperm donors of financial responsibility to children born from their semen are legally non-enforceable. Some circumstances turn a biological father into a Dad. True, the reasons why a New Mexico Appeals Court judge ruled that the biological father in question had to pay child support were understandable (he was not anonymous, saw the two children involved frequently, and had started to make decision-making demands). However, the new ruling may also affect sperm donors who count on the preservation of their anonymity when they donate sperm (in acutality, they sell it) to a sperm bank.
When, not too long ago, the powers-that-be in Vancouver decided that sperm donors should not be paid for their sperm, altruistic attitudes did not win the day. Instead the supply of sperm donors dried up. No money, no sperm. "No tickee, no laundree," as they used to say before political correctness made that term obsolete.
Now, as a "wave" of children born from donated sperm approach 18, there has been a movement afoot to get sperm banks to unseal records, and fathers who considered themselves purely biological may find themselves revealed to be "Dads." Sure, there's a big difference between an anonymous sperm donor and a friend who donates his sperm and then decides to have a relationship with the kids, but this distinction may be lost on potential donors. In fact, they may decide it's a bad idea to expose themself to future financial/legal involvement.
Contract/shmontract! I think they'll run for the hills.