I also appreciate the civil conversation. In just a few days, you are easily my favorite person to talk to with whom I disagree!
While I will admit that research seems to be divided on when the baby can actually feel pain (the article you linked even states as much: "Evidence regarding the capacity for fetal pain is limited but indicates that fetal perception of pain is unlikely before the third trimester."), I am encouraged to hear that you would consider it a deal breaker. I am starting to see you really are more to the center, with a small leaning to the left. You strike me as a classical liberal. Not sure if you would see yourself that way but that seems to be what I get from you, which is cool. Classical liberals are great!
I also admit my martian example is a bit extreme, but keep in mind, viability lends itself to that premise. I mean, I could also be misunderstanding your description of viability so to clarify, why don't we start there.
My understanding of the viability argument is that personhood is adopted once a person has self consciousness, autonomy or rationality. Assuming that is the definition you are using too, then the issue with that is that lends itself to infanticide and forced euthanasia. The reason why is if an infant, or even some toddlers, are left to their own devices, they cannot live. They aren't viable. In the same breath, as age sets in, there are a plethora of cases in the elderly who need assisted living to keep going and diseases which inhibit their rationality. My take is that they still have a right to live, even if their mind goes.
With that being said, I do want better understand your position. Would you mind either telling me if you agree with my take on viability or provide your own definition? I am sincerely interested to hear your side!