I thought I'd share with you my philosophy on the abortion debate-- always a good topic for a friendly, lighthearted conversation, of course.  But anyway, if you have a few minutes, and you want to think about this issue methodically and rationally, from a perspective you haven't heard, read this.   

Premise 1) The State must decide upon a specific definition of life's origin, a particular stage in development that serves as the line of demarcation between a human entitled to constitutional rights, and mere grouping of human cells.  This stage lies somewhere between gametes (sperm and egg) and a newborn baby.  This definition must be specific to avoid the deaths of any persons that should be entitled to rights.

Premise 2) The essence of being human-- the ultimate basis for human rights, protections, and services from the State-- is our qualitative experience.  The State is justified in protecting citizens from various sources of harm because of the qualitative experience of pain (I'm using this term broadly to include not only physical pain but any undesirable mental state such as sadness, fear, grief, etc.)  There is no other way to explain this other than that pain is painful, and therefore the State ought to protect against various sources of pain such as crime.  Thus, conscious beings have a vested interest in reality. Unconscious beings do not, because they are not subject to conscious experience. 

Constitutional and legal rights are ways to protect against various sources of suffering.  People would experience much more pain if constitutional rights, laws, and law enforcement did not exist (think of the resulting misery in a totalitarian society or a lawless state-of-nature.) 

Imagine, if it were possible, a human without the essential element of humanity, a "philosophical zombie".  He is not experiencing any qualitative experience, he is completely unconscious, but somehow he is able to function normally.  The orchestrated madness of his body continues: billions of neurons still fire away in his brain and provoke a chain reactions causing him to speak, his heart still beats, his behavior remains the same, etc.  When he is pricked with a needle he responds with a wince and yells 'Ow!', but he experiences nothing.  Existence for him is silent nothingness that wouldn't be any different if he didn't exist at all.

So why should the state protect him with laws when his own welfare does not even matter to himself? The welfare of an unconscious entity (I would not include people who are temporarily unconscious) is of no importance whatsoever unless it affects someone who is conscious.  Unconscious entities are in the same category as a table or a piece of glass- there is no reason to offer them rights because they have no vested interest in reality. 

Premise 3) For the first several weeks of development, the fetus is not conscious.  I am not writing this to propose when consciousness begins, because I simply don't know.  It's something science has yet to uncover.  Virtually nothing is known about how consciousness is produced, but there is no doubt that it emerges from the brain.  Furthermore, the elements of consciousness, such as emotions, sensory experience, and thoughts, are known to be produced in the brain.  Since brain waves are detectable in the developing fetus around week 13, it probable that the fetus is conscious by then.  But for a few weeks leading up to then, the fetus is a preconscious, complex series of organic molecules without any awareness or sensation.

Conclusion) It is unethical to abort conscious fetuses, it is not unethical to abort preconscious fetuses. Therefore, the State should protect conscious fetuses by outlawing abortions when it is considered possible that they are conscious.  Imagine you are a fetus in early development that has not reached consciousness yet, and your mother has decided to abort you.  If you are faithfully imagining what this procedure, your death, will be like for you, you will be imagining absolutely nothing.  You were experiencing nothing and you will continue to experience nothing.  Therefore, as I see it, no harm was committed in having the abortion.  A fetus aborted just before it achieves consciousness is no more tragic than a sperm that misses the egg by a millimeter.

Some will argue that unconscious fetuses deserve protection because they will eventually become conscious, and that they will develop into normal human beings.  I don't find this argument convincing, because obviously we should not be concerned with protecting every wasted sperm or egg cell to make sure that it develops into a life.  To respond to this by saying that sperm and egg should be excluded from protection, but that a fertilized egg cell should not, is arbitrary.  The ethicality of an abortion should be couched exclusively in the welfare of the fetus, and an unconscious fetus' welfare has yet to begin.  Aside from religious reasons, which I'm not even going to consider, there is no reason to grant special protection to a fertilized egg cell.  The desire to do this comes from a mental reflex, and instinct impelling us to begin honoring life at its official, biological origin.  It's an urge to find clarity and simplify our interpretation of the world, even when the reason to do so is not grounded in the welfare of the fetus in question. That, in my opinion, is unethical.