>unless you are comfortable saying that inflicting pain on infants is morally neutral.
Why not make your argument about chickens or pigs? I don't care if a chicken suffers before I eat it: it's dead. It was bred to die. That's not much of a moral quandary for me, to be honest.
Baby humans have a lot of potential, and we need them to make good decisions as adults. That doesn't happen when you don't care about children's pain. But it definitely also doesn't happen if you kill them.