"While the line of personhood is extremely hard to draw, it seems self-evident that it does not include an organism which can do nothing but absorb nutrients from its host in order to grow..." says Forum Lurker.
Hmmm... by that logic every human on life support is no longer a person. By that measure, every severly disabled human who needs regular assistance to continue living is no longer a person. There is a fatal flaw in the "parasitic" argument you posited.
If you think that a mother should be allowed to eliminate her unborn baby for various reasons, just say so. The American Heritage Unabridged Dictionary states "Life    1a. The property or quality that distinguishes living organisms from dead organisms and inanimate matter, manifested in fuctions such as metabolism, growth, reproduction, and response to stimuli or adaptation to the environment originating from within the organism."
By any application of that definition, life begins at the moment the egg is fertilized as the cells begin dividing immediately.
So where does that leave us? It leaves us at the point where we either agree that an unborn human may have its life stopped for whatever reason or we agree that an unborn human must be afforded the same protections by law as a previously born human. Its quite simple.
Now, before anyone says something again about the whole abortion/death penalty disconnect. I do not support the death penalty AND I do not support abortion.