for me there is an emotional response to this subject and a rational response, and i consider the latter more relevant. looking rationally at the question of abortion, given that there is no evidence of any non-physical entities (gods) that decide what is valuable in the universe, we humans are constructing a system of value. we have chosen to value our own species over others. this is rational and instinctual -- we value our family members over others because we share more genetic code w/ them. and we value humans over cats and dogs and tasty honey roasted pigs. it is also completely rational to value humans out of the womb over humans in the womb. what is good, in my opinion, is the minimization of human suffering. that is our moral imperitive. before humans have Hooksexup endings, they do not suffer. therefore ending the life of inchoate humans without the ability to feel is not inherently bad in my view -- particularly if not doing so will cause enormous suffering. it will cause unprepared parents to suffer, the unwanted child to suffer, and the people around the unwanted child to suffer. human suffering is bad. (read freakonomics for very interesting analysis of how legalization of abortional dramtically lowered crime in new york -- not guiliani).
on an emotional level, now that i have had a child, i do appreciate how conceptually upsetting it is to kill a fetus. they are so beautiful with their little pumping hearts and they contain the full potential to be human. it is an overwhelmingly beautiful thing to watch them grow through sonograms. i would be devestated to end the life of my own fetus -- and would resist doing so. HOWEVER i don't think its morally wrong. what we are morning is the loss of human potential. of course every night you don't make love to your spouse, you may be preventing the life of a beautiful creature. seriously. if ending human potential is what concerns us its rational to go the ridiculous lengths that the monty python crew does in "meaning of life" (every sperm is priceless).
i think removing god from the equation helps us to think sensibly of a what moral code we share as a speciies: minimization of human suffering is a noble mission -- more noble and less righteous than all the self-interested missions conceived of by various self-perpetuating religions. let's look out for sentient human life everywhere, and secondarily the lives of non-sentient humans followed by the lives of all living things.