"When William Marotta answered a Craigslist ad seeking a sperm donor, he was just trying to help two women start a family. [He] gave the couple several donations in plastic cups and signed an agreement giving up all his parental rights. He thought he would never see them again.

"But in October he got an alarming letter: though the women did not want him to be part of the child's life, the state of Kansas was suing him for child support."

Kindregan says that the law, written in the 1970s, is "clearly outdated," and needs to catch up "as the concept of family evolves into new forms."