I don't think it ever makes sense to say that an act, even one which deliberately brings about the destruction of innocent life , must be always and absolutely morally wrong.I sympathize, but I also think that this doesn't really work as a criticism of Anscombe's position. She does, after all, believe in God, and that God has categorically forbidden the intentional "sacrifice" of one innocent life. This makes a huge difference to what she would consider pragmatic and realistic.
Those who insist on this principle (sometimes called "the principle of double effect") seem not to appreciate the distinction between something being always undesirable in itself and its never being justified under any circumstances. We can all envisage consequences far worse than the destruction of a single innocent life: but following this principle, it would never be permissible to sacrifice this one innocent life (if this sacrifice were, in Elizabeth Anscombe's words, both "intended and foreseen") in order to save a hundred, a thousand or even a million such lives. I find this attitude incomprehensible.
Of course, I do not deny that taking a deliberate decision to destroy an innocent life involves very real and very grave costs and risks; but as long as we are honest with ourselves about these costs and risks, such decisions (which should be taken only at the highest level, and then only in time of war or other emergency) should always come down to a pragmatic and realistic assessment of the likely costs and benefits.
She also rejects even thinking about what one ought to do if (unrealistically) one 'had to' murder one to save millions. It is part of her faith that God is unlikely to put anyone in such a position, but this is not her main point on such matters. Her main point is that it is important for us to remain committed to refusing to commit murder, even though we could find ourselves in a situation in which it would be hard to think of a better course of action. I think she accepts that it is conceivable that there might be no better course of action (at least that an ordinary mortal would think of), but she objects to the suggestion that we ought to think about such things. They invite corruption. I find this attitude not only comprehensible but quite attractive.