An environment that is too hostile can not sustain life.
Here’s a useful picture of the human conception to implantation timeline:
“Birth Control” pills poison the womb, preventing implantation of the week old fetus in those cases where the pill did not prevent fertilization. For more on this, see the 28 Days on the Pill site.
George Johnston has written a useful survey article: The Bitter Pill.
Here’s an article which realistically discusses problems with Natural Family Planning.
On the broader issues of value, see the encyclical Humanae Vitae.