Quoted For Truth, from this post.

There is no rational secular argument against abortion. In order to put one forward, you would have to argue that a foetus should be considered to possess superior personhood and a greater right to exist than that of the adult woman who is carrying it. That a non-conscious ball of cells is more a person than a woman with hopes, dreams and ambitions. You would need to assert that the right to bodily autonomy is not absolute, but is actually a limited right that is not afforded to women once they fall pregnant – that pregnant women are second class citizens who are to be denied any right to self determination. It would be nothing less than an argument for procreative slavery. 

Without ridiculous religious claims of magical ‘ensoulment’ of foetuses that afford personhood in vitro – coupled with a refutation of the notion that no person can claim rights in the flesh of another, perhaps the most dangerous precedent imaginable – there is no possible moral or rational basis on which to argue that any of this is a good thing.

I'm not an atheist, but there are a number of good blogs at Freethought Blogs. Pharyngula is one of them.