Given our first assumption, a condom user (who makes no distinction between HF [high fertility] and non-HF periods) can count on one embryonic death for each unintended pregnancy. A rhythm method user, however, should count on two to three embryonic deaths for each unintended pregnancy. Assuming a success rate of 95% for condom usage, we can count on an expectation of .5 pregnancies in 10 years. Hence, the expectation of embryonic death is .5 per ten years for a condom user, which is substantially lower than the expectation of two to three embryonic deaths per ten years on the rhythm method. Even a policy of practising condom usage and having an abortion in case of failure would cause less embryonic deaths than the rhythm method.
[...] One could simply conceive of this whole argument as a reductio ad absurdum of the cornerstone of the argument of the pro-life movement, namely that deaths of early embryos are a matter of grave concern.