Its clear that fetus doesn't magically become a person by passing through a woman's vagina. It is clear that if you aren't for killing born babies, then you shouldn't be for killing a late term fetus. It should be considered murder unless the mothers life is at grave risk.
Its also clear that a sperm entering an egg doesn't make a person either. Yes, for religious or philosophical reasons, a individual has the right to believe that is a person but law that applies to everybody should be based on our best scientific knowledge and social norms. IMO, until we have evidence that the zygot, embryo, or fetus is self-aware or at least has some brain activity that correlates to what we consider thoughts (as opposed to reflexive stimulus response), then the fetus is not a baby, but rather a potential human. I think its safe to say that an abortion in the first few weeks of pregnancy is just removing tissue. But of course, many people will feel differently, and their personal choice should also be supported.
The time in between is a grey area....nobody knows. Society should protect the fetus unless there is good medical reason to abort...severe birth defect or mother's health.
That said, I think the trimester system the Supreme Court addressed is very reasonable.
Many of you will disagree with me. That is ok. This is America, and freedom of belief should not only be tolerated, it is essential.
One thing for sure, I think that preventing unwanted pregnancies before they happen is the best solution. This comes from education, availability of birth control, and socio-economic programs.