BTW are you familar with the usual philosophical arguments in this debate or are you just reasoning from your own views?
If I weren't reasoning from my own views why would I care to tell you anything as I could just ask you to read a book? I have of course read about this, a bit here and bit there, but found it mostly boring because those people who usually tries to reason out of this doesn't understand what emotions and sacred ideas (like those of Humanism) are. They seem to think that abortion is like a geometrical shape you can prove a theorem with. (I liked the alternative feminist approach to this the best, but forgot the name of it. It's a bunch of women who ponders on mothers' love and stuff like it)
The reasons why laws in most countries aren't absolute is because there is such a thing called emotions and there is such a thing called sacred ideas, and they are there for a reason (to guard us from losing a sense of what care is). In my point of view a foetus is a person because already from the point the brain develops it contains information that is "like me". In my point of view killing a foetus is like killing myself, as if that part of me didn't matter.
It's got down to the question of: does a tree falling in a forest make a sound? Does the human beings that I'm about to destroy with my nuclear bomb exist? I could say "no" because I didn't see them, I didn't hear them, and they may even be written out of history so I never have to wonder about them again. What stops me is the thought: that is *me* out there, thousands of me's. I don't want to kill me.
That is how a sacred idea works, that is how emotions work. And it's even more real and more valid than any claims on what *defines* a human being. If you can argue, then just don't do it. (Though as I've pointed out there is nothing absolute with this as well, disasterous situations should be avoided).