A fetus is human, and alive. No question about it. But it's not a person, and its life is not valued in the same way as a person.
If a group of judges or the government decided your life had less value (for some reason, your faith, your gender, your health, your race, financial status.. etc.) than the other 100% real persons, would you feel the same way?
Abortion has far more to do with POLITICs than actual humanity or "Life Science".
Let me give you what I feel is a pretty good analogy. DUI checkpoints are clearly violative of the 4th Amendment's prohibition against unreasonable searches and seizures. In ruling that DUI checkpoints are legal and may be maintained by law enforcment agencies, The Supremes admitted that DUI checkpoints violate the 4th Amendment, but allowed their use in spite of this on the basis of a
policy decision, namely, that the slight inconvenience to motorists caused by the brief intrusion into their day (or night) by being forced to go through a DUI checkpoint, is outweighed by the greater good to society in general by taking drunk drivers off the road.
I think this analogy applies to the issue of abortion. As I have said previously in this thread, I don't think there is any question but that life begins at the moment of conception. The current law on abortion appears to be based pretty much on the same logic as the DUI decision - a policy decision.
Policy decisions say something like: "Look - we understand the argument you are making against what we are about to do, and we concede the viability of your argument. However, in spite of all that, we are going to rule against you for policy reasons. Even though you are 100% correct, we feel that, after weighing both sides of the issue, it is a better policy to do it the way we want rather than the way you want."
Applied to the abortion question, it would look like this: "Even though we agree that life begins at the moment of conception, there are other interests to be considered and, taking those other interests into account, we rule that the life that began at the moment of conception must, to a certain degree, take a back seat to those other involved interests."