I think there is an important debate to be had on this topic, but sadly this does not appear to be it.
I think the discussion (not just on here, but in society as a whole) suffers from the fact that the terms of the debate are so poorly defined. So I'd guess all of us would agree that infanticide of a newborn is morally wrong, and pretty much all of us would agree that what the Americans call 'partial-birth abortion' is wrong. And I suspect that the overwhelming majority would have very grave reservations about third-trimester terminations, even for apparently very compelling reasons such as major abnormality of the foetus or serious mental illness of the mother. But I would also guess that most posters here (though clearly not all) would accept, as do the vast majority of the British public, that a first-trimester embryo does not have the same status, and would support properly-controlled early termination.
Yet unless and until there is a compelling evidence base for the point at which a single fertilised egg becomes a proper human being, it is impossible to have a productive discussion on the ethics of termination because everybody is arguing from a different starting point. And the Catholic church has done itself no favours by conflating the morality of contraception with that of abortion, when there are clearly very different issues at stake both intuitively and logically.
I am a Catholic, though by no means an uncritical one, and I think that there is a continuum between the single cell and the newborn baby, which leads me directly to being deeply uncomfortable with the idea of abortion. I sincerely hope that if I were in the position of being pregnant under catastrophically unsuitable circumstances that I would have the courage of my convictions, though I know one can never be sure until in that position for real. I am also aware that my position springs at least in part from a Catholic worldview (not just because the Church says so -- I have no probs with contraception, it's a separate issue), and that one can construct perfectly valid arguments against my position. So I would in no way be seeking for my viewpoint to be represented in legislation, since it's one that most people don't share.
I'm very frustrated by the way the debate on this topic usually goes, both on here and in RL, particularly the way that many Catholics quickly dig themselves into a viewpoint that is all too easily characterised as bigoted and reactionary, while the people who make sound logical arguments for abortion get side-swiped by the fact that there are clearly individuals out there who are irresponsible about contraception and inappropriately cavalier about abortion in a way that does the cause no favours.
It is an important debate -- I'd be interested to hear eg. the pro-abortion people's views on what the cut-off point should be for abortion. And how you think access to terminations should be controlled, assuming you don't think it should be available on demand? And in return could everyone accept that Catholics can hold strong views on this topic without necessarily wanting to come over all southern-Baptisty? [quizzical but mildly hopeful smile]
I thank you.