Is Acting on the Embryo Morally Dispositive?

Here is the Finnis, Grisez & Boyle article referenced by Karen Stohr (thanks to Antonio Manetti for the link).  And here is a helpful excerpt from their discussion of the moral distinction between a hysterectomy and craniotomy:

[T]he hysterectomy is performed "upon the woman," the craniotomy "upon the fetus." We reply: this difference does not show that craniotomy is direct killing. A counter-example makes this clear. All those acts of self-defense of the kind that Aquinas shows need involve no intent to kill and no direct killing are nonetheless performed "upon" the person killed.  And in general, the fact that an act is done to (or "upon") X for the sake of Y, or to Y for the sake of Y, provides no criterion for distinguishing between what is intended and what is accepted as a side effect.

This underscores my own (much less educated) skepticism toward the lines drawn on the issue of ectopic pregnancy.  If we're going to invoke Kevorkian, the remove the tube / remove the embryo distinction seems akin to attaching moral significance to the difference between Kevorkian assisting a suicide by lethal injection and assisting a suicide by bulldozing the victim's house while she is inside.  The death is certain to result in both cases and the actor's intent is, as far as I can tell, identical.  So why does it matter if I bring about the death by acting upon the person or by acting upon the container in which the person is located? 

Rob