I think we are forgetting about the person actually giving birth here...the emotional attachment a mother has to their children is a bond NONE of use can fathom. Imagine giving birth to your child, and then having it destroyed. I cant even imagine the horror i would suffer going through that. Its one thing when its a fetus, it isn't seen by the mother, and she didn't just go through all that labor getting it out.
There are a lot of variables that go into this...not just the final outcome. Human emotion is the strongest driving force behind our actions, whether we want to admit it or not. Its easy for us to sit here, as men, to say "meh, just kill it". Its another thing, as a future father, to be there when your child is born and have it taken away from you immediately, not matter how many imperfections it may have.