If a woman's life is in jeopardy, you are fine with abortion. You allow for that choice. The same question could be asked, "What did that baby do to deserve death?"
This is an application of the ethical principle of double effect, which posits that it is permissible to cause an unintended harm in order to prevent another, even if the unintended harm would not be permissible otherwise, and if the intent is not to cause the unintended harm but to prevent the other one.
An example of the principle is self-defence: being forced to commit homicide to stop a homicidal maniac from murdering you. You would be the murderer if you killed the maniac in cold blood, but killing him as an act of self-defence is permissible if necessary. The life-of-the-mother exception is basically an application of this. If, without the abortion, the mother will die (and then, so will her child), then according to the principle of double effect, it's permissible to induce an abortion--not to kill the child, but to save the mother.
Otherwise healthy pregnancies caused by rape or incest do not threaten the life of the mother. Indeed, many such children are born and loved and cherished by their mothers regardless of the circumstances of their birth, so it's not even a sure thing that their psychological well-being is harmed. Killing an unborn child is not a proportionate response to potential harm to the mother's emotional or psychological well-being. It's not the moral equivalent of saving her life.
Additionally, those three hard cases make up a very small minority of abortions. As abcaines pointed out, they're used by pro-abortion advocates as fig leaves for their agenda of legalizing abortions for any reason, at any stage of pregnancy. Hard cases make bad law.
I dont believe we need to let this cause a double-jeopardy leaving the rape/incest victim with guilt.
If we don't want to leave a rape victim with guilt, how much more should we want to protect her unborn child, who is equally guiltless?