At what point is a foetus alive? This is something that is not adequately discussed in my opinion.
Its alive from day 1... it might not be sentient, it might just be a very small developing organism but its still alive. You've then got a gradual process by which it becomes more and more like a baby... and a stage where it could be born prematurely and still survive... Other than the act of actually giving birth there is no magic line in the sand where you cross a specific point and it magically becomes a baby...
To refute Dowie's earlier point about having a **** causing millions of death, this is not the same. No amount of sperm or eggs on their own is going to result in pregnancy and thus there is no chance of a human being.
Not on their own but a small sack of cells killed off in a chemical abortion or with a morning after pill isn't that much different. I think at later stages abortion does become very dubious but at early stages it.
A woman gets rid of an egg when she had a period... if one sperm has entered and its divided a few times then is it massively different? I really don't think its particularly sacred at that point... there is a grey area in between that point and giving birth where a line should be drawn rather arbitrarily but its really a bit of a grey earlier. Ideally abortions should be early stage and easily available to any woman who wants one.
Some have suggested it even cuts crime:
http://pricetheory.uchicago.edu/levitt/Papers/DonohueLevittTheImpactOfLegalized2001.pdf