Why the Church is so Focused on Abortion, et al
The battle over birth control, abortion and stem cell research is about more than just sex or the life of the blastocyst or fetus. While these are important issues, the reason the Church feels such a stake in this battle is that it says a lot about the very nature of the human soul.
The Church is wed to the idea that life begins at fertilization. This is a fairly recent development, as classical metaphysics, indeed Thomas Aquinas himself, taught that the soul was imparted at a later, sometimes much later, time. Aquinas thought that when the fetus began to move, there was proof that a soul was present. The Anglican Communion posits that implantation or gastrulation is the marker for ensoulment - a position that actually makes sense because before gastrulation human-bestial hybrids still develop. One can assume that God does not impart a soul to such hybrids, or that he adds an additional soul when twinning occurs, but this comes under the heading of making God do tricks to justify the Popes take on biology. This does not work as a matter of natural law reasoning.
This is a minor point of debate which impacts whether the Church is credible on birth control and stem cell research (which, as I have said before, it isn't - the Church's authoritative position would be strengthened if it would concede the biological point and move on). However, it only scratches the surface of the deeper question.
The deeper question, which scares the Hell out of the bishops, is whether people believe in a soul at all. If there is no soul at the front end then there is also no soul on the back end. If the soul is not cause it cannot be immortal. Without immortality with God, why bother with God at all, or with any of the Sacraments of the Church. They simply can't concede the point.
The soul has to be causative, even before the child develops the capacity for rational thought. The alternative is either no soul at all or a soul that is developmental - meaning one that grows out of experience and language rather than something that drives the organism. The sticky part is that neuroscience seems to show no "ghost in the machine." The soul, if it exists (and again, I believe it does) is totally integrated with the brain. This need not cause difficulty, as the brain and the cells which give rise to it, are totally involved in the development of the embryo after gastrulation - however they are not involved before it because before gastrulation the cells are not differentiated.
Like I said above, the Church would win by conceding the point on fertilization. Sometimes admitting when you are wrong actually increases credibility. Not doing so is generally regarded outside of the hierarchist world as being faulty reasoning.