The concept of viability is a bad argument for abortion. The reason being is that viability is subjective. What actually counts as viable? What actually counts as inviable?
The fact that a fetus (4th declension Latin noun for "baby") isn't viable before a certain stage of pregnancy is a misleading argument. The baby is viable utilizing the life support system provided by her mother.
The real issue then is the fact that the baby is dependant upon her mother for survival. That actually IS a form of viability. One such definition would be, "capable of surviving or living successfully, especially under particular environmental conditions."
I recognize that medically speaking the argument of viability is the capability of survival outside the womb. Which, of course, can happen prior to full term. But again, that's too subjective.
Since, given certain conditions like the life support of the mother, a baby is surviving. Survival through dependability is still survival. And the fact is that anyone then who needs someone or something to survive is still viable.
To argue that a fetus isn't a human because of perceived, subjective viability is to diminish the humanity of a large number of people. Imagine the implications of this argument on people who are dependent upon medicine or caretakers in order to live.
Instead, what the Abortionist needs to do is to prove that the fetus commonly does not result in another, distinct DNA carrying, human being.
In other words, if the process that a woman falls into after sexual intercourse that requires the abortion procedure is not the production of a new human being then it would logically follow that the result of this process would not be a human being.
And therefore, the concept of abortion makes sense as a woman caring for her body. And it would be an issue of bodily autonomy and a woman's right to consult her doctor regarding her healthcare.
However, if the process that a woman incurs as a result of sexual intercourse is the production of a human being that results in a human being then "health care" is a misnomer and to terminate the pregnancy is tantamount to murder.
Obviously, the latter is the case. This is just for the sake of argument.