If you are already on the pro-choice side of the house, feel free to skip this part. After all, if life begins whenever you define it (instead of, oh I dunno, at the beginning) then the fact that The Pill causes abortions won’t be of any consequence to you. But for the sane among us, educate yourself:
How the Pill Works as an Abortifacient:
The Pill as it exists today does not just prevent life from ever coming into being, it destroys it after it is created. A human person is killed by The Pill.
http://www.patheos.com/blogs/badcatholic/2011/10/10-reasons-the-pill-sucks.html