I've read some doozies in my day, but this one may have to go to the top of the list. In his latest book, Faith and Health: Religion, Science, and Public Policy (Mercer University Press, 2008), University of Louisville ethicist and Baptist minister, Paul D. Simmons, writes: "Bernard Nathanson, narrator of The Silent Scream, was once a Catholic priest and believed an embryo to be a person based on religious teaching. Now that he claims to be an atheist, however, he says his belief has nothing to do with religion."
Actually, Dr. Nathanson, who was born to Jewish parents, was once an abortionist (and atheist) and served for a time as director of the largest abortion clinic in New York City, the Center for Reproductive and Sexual Health. He also helped found the National Abortion Rights Action League. He became prolife and remained an atheist for over 15 years before he was received into the Catholic Church on December 8, 1996. In the book in which he provides an account of his break with the abortion rights movement, Aborting America (1979), Dr. Nathanson does in fact offer a secular defense of the unborn's personhood. His 1996 book, The Hand of God, tells the story of his conversion to the prolife perspective in the late 1970s up until the time right before his conversion to Catholicism in 1996. The book includes an Afterward authored by the Rev. C. J. McCloskey, III, the Catholic priest instrumental in leading Dr. Nathanson to Christ and His Church.
Coincidentally, nine years ago I published in the Journal of Church & State a critique of Professor Simmons' work on abortion. You may download a pdf of the article here. Much of that article was incorporated into portions of chapter 3 of my book Defending Life: A Moral and Legal Case Against Abortion Choice (Cambridge University Press, 2007)
(Update: It should be noted that Dr. Simmons' views on abortion do not reflect the position of America's largest Protestant denomination, the Southern Baptist Convention. The SBC is unequivocally prolife).