The distinction about when a pregnancy begins is important.
If pregnancy begins at conception, then hormonal-based methods of birth control would be considered abortifacient as they are designed to prevent implantation.
If pregnancy begins at implantation, then hormonal based contraception doesn't end a pregnancy-- it only prevents it. If there's no pregnancy, there's no abortion, right?
Then you have to explain away that pesky term "chemical pregnancy" in which there is a conceptus, but no implantation.