Boss
Take a Memo:
Except viability has nothing to do with fending for one's self, and providing one's own needs. It specifically defines the ability of a fetus' biological functions to operate without the host organism - respiration, digestion, circulation, etc. And you know this. However, this conflicts with your contention that it is synonymous with an actual infant, so you want to pretend that viability is referring to something that it is not.
You can't tell me exactly when a given fetus is able to meet your criteria and you can't guarantee any absolute result. Just because a fetus has passed your arbitrary threshold doesn't guarantee the can meet your criteria.... in fact, may fetuses don't. Some fetuses are born, become infants and have to be put on life support in order to make it. So there simply isn't a magical line in the sand where a fetus becomes "viable" and it is totally dependent upon the conditions and about a million different variables that cannot be predicted or assumed.