Rhythm method criticised as a killer of embryos

From an article of the same title by Alison Motluk on NewScientist.com:

The range of birth control choices may have become narrower for couples that believe the sanctity of life begins when sperm meets egg. The rhythm method, a philosopher claims, may compromise millions of embryos. "Even a policy of practising condom usage and having an abortion in case of failure would cause less embryonic deaths than the rhythm method," writes Luc Bovens, of the London School of Economics, in the Journal of Medical Ethics. With other methods of contraception banned by the Catholic church, the rhythm method has been one of the few options available to millions. In using the rhythm method, couples avoid pregnancy by refraining from sex during a woman's fertile period. Perfect adherents claim it is over 90% effective - i.e. one couple in 10 will conceive in an average year. But, typically speaking, effectiveness is estimated at closer to 75%. Now Bovens suggests that for those concerned about embryo loss, the rhythm method may be a bad idea. He argues that, because couples are having sex on the fringes of the fertile period, they are more likely to conceive embryos that are incapable of surviving... Bovens calculates that, if the rhythm method is 90% effective, and if conceptions outside the fertile period are about twice as likely to fail as to survive, then "millions of rhythm method cycles per year globally depend for their success on massive embryonic death"... "If you're concerned about embryonic death," Bovens says, "you've got to be consistent here and give up the rhythm method."