I generally avoid these arguments...
But two points.
First, there seems to be an underlying assumption here of the importance of human life in the grand scheme of things. Any question of abortion, for me, hangs on the question of the importance of human life. I tend to see us (humans) as another evolutionary mistake, just like any other species. Consciousness, too, is an evolutionary mistake that allowed us to stop adapting to our surroundings and gave us awareness of our surroundings so we could adapt them. If humans are just another species, and consciousness does not give us a moral or ethical imperative to spare human lives, then what is the real question here? I think one has to weigh, then, the positive and negative effects on the potential person's life, and the lives of those that are creating it.
Which brings me to my second point. In the end, i never have to have an abortion, not having a womb and all (i tried letting the fetus gestate in a box, didnt work). So i never have to atually make the decision. I think its important to realize that, as much as we discuss the positives and negatives of abortion, its the woman who has to do it. She has more at stake than anyone else. I think, for this reason, in the end, it should be each individual woman's decision. I rarely fall in line with political bandwagons and the party-line rhetoric of these "issues," but in this case i think the "Pro-choice" line is right - generally not for the same reasons, but because in the end, im not going to tell a woman she cannot do something with her body, or that she should. If i were to be in the predicament, i would definitely have my opinion, but in the end, its the woman's decision.