This page presents some thoughts related to the abortion debate without, I hope, taking sides.  A potentially important question in the debate is "At what stage of development does a fertilized egg become a human being?"  To answer this question we need to know whether human beings have souls and, if so, at what stage of development the soul enters the body.  "Soul" here is understood as something distinct from the body that enters the body at some stage of development.
  
First, suppose souls do not exist.  Then the fertilized egg contains all it needs to develop into a human child given the proper environment.  Thus, someone who does believe in souls should accept the idea that a fertilized egg is a human being.  Also, some birth control methods prevent implantation of fertilized ova and so deny these human beings the envirnoment they need to develop into healthy children.  Maybe one should oppose such devices, perhaps even as strenuously as one supports other measures that help fertilized ova grow into healthy children such as education in methods for preventing STDs (which can cause birth defects), support for reasonable wages so pregnant women can be in good health and obtain proper nourishment, support for strong enviromental standards since fetuses and often more sensitive and support for measures abroad such as inexpensive AID drugs for Africa.  At any rate, atheists who support abortion need to do a bit of fancy footwork.
  
Second, suppose souls do exist.  Until a soul is present, the fetus is not a human being and so could reasonably be subject to different treatment.  When does the soul enter the fertilized egg?  There are a variety of answers.

• One answer is when rationality is present, which is considered to be around 6 years of age. Since few present day Americans are likely to accept the view that young children are not human, so we should look for "better" answers.
• At the other extreme is the answer that the soul enters at the moment of conception.  From a Christian viewpoint, this idea is abhorrent.  Many fertilized eggs fail to implant and many more abort early in pregnancy, some so early that the woman does not even know she was pregnant and merely thinks she had a late period.  If these are all human beings, it is a clear indication that God cares little for human life, a notion abhorrent to Christianity.  Thus we look for "better" answers.
• Other answers are sometime after the first trimester, some say as early as when the fetus moves ("quickening"), others as late as the moment of birth (however that moment is decided).  If this is the case, early abortion may be acceptable.  At the least, Christians who call early abortion murder need to do a bit of fancy footwork.