God is completely good, he can never do evil. In order to kill everyone in
infancy without doing evil, he would have to accomplish this through the means
of some other agent’s free action. This
is because earthly human life is a good, and God’s nature as wholly good
would thereby preclude him from destroying such life without a morally
since the infants in question are, of course, innocent, his goodness would
preclude him from ending their earthly life directly. Thus the free action of another would be
required if he were to carry out that particular action. But in order for him
to allow that, he would have to allow at least some free agents to live
past infancy (so that they could kill the rest of those in infancy). But if he
does that, there is no non-arbitrary way to decide who gets to be
killed in infancy (and thus who goes to Heaven) and who does the killing of
those in infancy (and thus who is not guaranteed Heaven by dying in infancy).
Thus he cannot kill all those in infancy so as to maximize the number of
those in Heaven.