It's pretty late in the thread, but I will state my opinion here all the same. And no, I didn't read this thread past the first page, so I may well be repeating what others have already said.
First of all, I am not religious. I mean, I am, but I am not Christian. I am a Discordian, and my religion is all about choice and how each one of us sees reality differently from others. But I am still strongly against abortion.
This is why: for me, the moment of conception is really defining, for the simple reason that the new-formed embryo already has all the genetic information that will determine who that person is. Before conception, it's all pretty much in the air, depending on which spermatozoid is going to "win" the race, but when that race is over, the new individual is already defined. It doesn't matter it's just a bunch of cells, those cells are already on a very strict process of evolving into a specific person. And interrupting that process, from where I stand, is the same as interrupting any other life, i.e., it's killing.
And before anyone yells "you are a man, what do you know about the subject? blahblahblah", I was forced to analyze the matter pretty closely at a young age, when my girlfriend got pregnant twenty years ago (we were both sixteen). We both considered an abortion, but decided against it simply because we couldn't live with ourselves if we went through with it. My son is now 19 years old and one of the best things that happened in my life, despite all the hardships I went through while raising him. So I say: if you act irresponsibly by having unprotected sex (like I did), you have to be prepared to take responsibility for the results of your act. Hiding behind the "choice" argument doesn't change the fact that you are killing an innocent person without giving them a chance to defend themselves.
Matthew Geskey said:
Now, I think that freedom is the ultimate good, and preventing life is removal of all freedom. So abortion should be allowed if the "child" agrees to give all of his freedom to his mother.
I wish I had read your post before writing mine. You put things in such an obvious light that I feel my post is useless now.
Note: In my ramblings up there I didn't consider the matter of abortion in cases of rape or if the mother and/or the child wouldn't survive birth anyway, because those are exceptions, not the rule. Those would be the only valid reasons to have an abortion, in my opinion.