Some Catholic History
Catholic Positions Concerning Abortion: The Catholic Church has always opposed all abortion, but for most of its history did not punish with excommunication if an abortion was performed before the time of quickening, ± some for male versus female. There was an early temporary ban from the time of conception for three years from
1588 to 1591, but it is not clear what the thinking was at that time. A common prevailing view was that early life starts from a miniature form of the adult, but some must have been aware that early miscarriages or abortions produce a tiny jelly blob with no bone and no recognizable shape.
The existence of cells was not known until the early 1800s and the fact that there are such things as sperm and egg until the mid 1800s. Then around 1886 science began to suspect that future inheritance of the individual is cast by union of chromosomes from sperm and egg. The Catholic Church ban on abortion from the time of fertilization came three years later, and many countries soon passed secular laws of the same nature.
This was not a reassessment of abortion. It was change in view of when there is a physical being with soul and hence when there is something to protect. Early embryology had provided an answer to the age-old theologic question of when life begins.
Catholic Theology Concerning Birth Control: The Catholic conclusion that birth control is sinful and priests must be celibat follows from the Garden of Eden scripture plus the concept of "Original Sin." All decedents are punished for the sin against God by Adam and Eve and not just in the original Jewish sense of expulsion from the garden of plenty, but by having Sex cast upon humans as punishment on earth. In this view sex did not exist in the perfection before Original Sin and will not exist in heaven. Sex on earth is an "inherited sin" and therefore sinful in all forms except for procreation in marriage.
A New Theme Concerning Birth Control:
A more common reason used today for why birth control should be avoided is that pills and IUDs prevent implantation and kill embryos (which is bad because they are endowed with soul). But there are two technical complications with this point of view. First, full-time nursing is a form of birth control using the same hormones as the pill and subject to the same condition under which it prevents implantation. Schedule must be maintained for both.
Also, the primary actions of the pill and of IUDs are to block ovulation and kill sperm - thus preventing nature's high loss of fertilized eggs. Except for the very young and fertile, not using birth control causes the natural loss of about 4 to 8 times as many fertilized eggs as abortion and hundreds to thousands times more than the very few that might be lost with birth control or even the Plan B morning-after pill.
If the objective is to save embryos, the best way to do it is to use birth control. If the objective is to argue against birth control, a better way to do it may be to use the older Catholic theology.