Is Natural Family Planning Necessarily Innocent?
According to a recent study (technical article here), Natural Family Planning (the “rhythm method” with minor improvements to make it actually effective), works partly by decreasing the fraction of eggs fertilized and partly by decreasing the fraction of fertilized eggs implanted. In other words, if fertilized eggs should be regarded even a little bit as human beings, that would mean Natural Family Planning increases the abortion rate.
First, we should remember that not every theory pans out. In particular, if the Roman Catholic Church is your tradition, you should not yet feel obligated to leave.
Second, if you were planning to become Catholic but the Roman Catholic Church is not your tradition, you should at least wait until this is sorted out, if ever.
Third, there are religions where Natural Family Planning is not acceptable. In particular, Orthodox Judaism holds that marital relations should not resume until after menstruation is over for a week. That will cut down on the number of nonviable embryos produced. That, of course, means that Jews who converted to the Catholic Church out of opposition to abortion should, of course, return.
An essential disclaimer for that last point: I am not an Orthodox Jew, I am Orthodox sympathetic. I agree with some of their reasons for being dubious of Reform/Conservative/Reconstructionist/Renewal Judaism. On the other hand, some parts of Orthodox Judaism seem a bit preposterous. One of the preposterous elements looks much more reasonable now. (I suppose I'll find there is a reason why kosher for Passover pet food is imperative next.)
Addendum: I suppose it's necessary to point out that enforcing a potential law against sex at the wrong time of the month really would violate privacy. Besides, by the time this research has been verified, the Catholic Church will have a different dogma.
Of course, I support the right of pharmacists to refuse to sell calendars.