Controversy is swirling over an ethics expert's opinion that it's O-K to let parents choose the sex of their babies. John Robertson is ethics chairman for the American Society for Reproductive Medicine, which sets fertility clinic standards. He says it is ethical for certain couples to choose the sex of their children for non-medical reasons. An infertility company sought Robertson's opinion. But, it's caught many reproductive specialists by surprise. Some say sex selection is a form of discrimination. Others worry it could lead to choosing children on the basis of other traits, like coloring or intelligence. The ethics group says the letter is Robertson's opinion, not a ruling, and its policy stands. It discourages sex selection.