Those who took offence because they know and love a person with Down Syndrome, and who thought I was saying that their loved one had no right to exist. I have sympathy for this emotional point, but it is an emotional one not a logical one. It is one of a common family of errors, one that frequently arises in the abortion debate. Another version of it is The Great Beethoven Fallacy discussed in Chapter 8 of The God Delusion. I combated it in a tweet as follows: Theres a profound moral difference between This fetus should now be aborted and This person should have been aborted long ago. I would never dream of saying to any person, You should have been aborted before you were born. But that reluctance is fully compatible with a belief that, at a time before a fetus becomes a person, the decision to abort can be a moral one. If you think about it, you pretty much have to agree with that unless you are against all abortion in principle.The definition of personhood is much debated among moral philosophers and this is not the place to go into it at length. Briefly, I support those philosophers who say that, for moral purposes, an adult, a child and a baby should all be granted the rights of a person. An early fetus, before it develops a nervous system, should not. As embryonic development proceeds towards term, the morality of abortion becomes progressively more difficult to assess. There is no hard and fast dividing line. As I have argued in The Tyranny of the Discontinuous Mind, the definition of personhood is a gradual, fading in / fading out definition. In any case, this is a problem that faces anybody on the pro-choice side of the general abortion debate.