First off, I believe that human life starts at conception. Because how could it not? I also think that it's impossible to regard that human life as a person for purely practical reasons. We don't live in a universe that allows us to do that.
"Up to 50 percent of all fertilized eggs are lost before a woman's missed menses."
Conception: How It Works
"Around half of all fertilized eggs die and are lost (aborted) spontaneously, usually before the woman knows she is pregnant."
Miscarriage: MedlinePlus Medical Encyclopedia
"as many as 50% of all pregnancies end in miscarriage -- most often before a woman misses a menstrual period or even knows she is pregnant. About 15-25% of recognized pregnancies will end in a miscarriage."
http://www.webmd.com/baby/guide/pregnancy-miscarriage
Now let's say we grant a fetus person-hood from conception, as many pro life supporters want. That would mean
criminalizing both IVF and miscarriages. Picture this scenario.
If I were to ran over any person, child or adult, with my car in the mall parking lot, there would be an investigation. I would be tested for alcohol and drugs and if I were found to be at fault I would go to prison, most likely for involuntary manslaughter. (Correct me if I'm wrong about this)
Or consider this news story:
Discovery of toddler's body in yard leads to couple's arrest
The fact that a child's body was found on the property was cause to make an arrest.
Now if we afford a fetus the same rights as that person who was run over in the mall parking lot, then every time a woman miscarries there would need to be an investigation into the cause. You can't just throw your hands up and say "well, it was probably an accident." Because that would be conceding that a fetus doesn't have the same rights as a person.
And how do you differentiate between a spontaneous abortion and a self induced abortion? (A self-induced abortion or self-induced miscarriage is an abortion performed by the pregnant woman herself outside the recognized medical system. )
You can't lock up every women who has had a miscarriage. That would leave almost the entire female population in prison and create a dystopian police state.
If you want to be consistent, there needs to be created a system were pregnancies have to be registered, and monitored with mandatory checkups of any blood loss by a doctor,...
But this would be practically impossible. Every pad, tampon would become a crime scene investigation. Most states don't even have enough resources to test rape kits. Thousands get thrown away untested. So how will they test every failed pregnancy?
Imagine a couple trying to conceive, they want to start a family. Statistically they have a high chance of killing a zygote that fails to implant as you can see from the statistics I mentioned. Do you want them to be the subject of a criminal investigation? If the answer is no then a zygote isn't a person.
And that's why I don't believe in granting person-hood starting from conception, from a practical standpoint.
A few additional points
If you believe God created this universe, you must also believe he made it so that it is impossible to regard a fetus as fully human.
For hundreds of thousands of years of human evolution, God was apparently ok with a high death rate of children. The reason people had so many children in the past is because so many of them died. If you want the stats on that look
here.
"A century ago every third child died before it was five years old"
Thanks to advancements medical science the mortality rate has been drastically reduced to something like less than 1%.
When abortion will finally be outlawed, it will be because medical science will advance far enough that a fetus can be made viable outside of a women's body in some kind of artificial womb, and not because of religious dogma or people screaming at women outside of a clinic.
