I'll pass over that piling heap of confusion that passes for theology including errors that are proximate to heresy and repeat, once again, that even inculpable ignorance does not supply for a defect.
You seem to refuse to realize that if there is no culpability, there is no mortal sin and thus no punishment for mortal sin (Hell). As I've established, the Church teaches that those outside the visible structure of the Church CAN be saved.
Therefore it is simple logic and moral theology analysis to conclude that athiests acting in good faith are in ignorance and thus not culpable and able to be saved.
Santo,
Invincible ignorance only applies to ONE SIN: The mortal sin of unbelief. By saying someone is invincibly ignorant of the truth, it means their unbelief is not criminal.
But that does NOT constitute an infusion of sanctifying grace, without which NONE are saved.
They are in Original Sin, and mortal Sin. They have their conscience, and the natural law. If they WILLFULLY defy their conscience, even if it is badly formed, on a serious and grave matter (masturbation, adultery, killing, theft, etc.), which are universally acknowledged as GRAVE, it constitutes a mortal sin.
So then, how do they receive sanctifying grace? Does GOd mMAKE them saved just because they are ignorant? No.
God does not violate free will. The Person who lives in a state of invincible ignorance MAY be saved: If his ignorance is dispelled and the truth is revealed!
The invincibly ignorant have NO MORAL MECHANISM whereby they can recognize the grace of God and freely respond to it. How then, can they be saved? Like St. Paul says; "How can they believe unless they have heard, and how can they hear without a preacher?"
If you insist on it, explain it in a hypothetical real world desert island circuмstance. Explain to me how this can work.
The invincibly ignorant are saved the same as Jews: Repudiating their former faith and converting to the Catholic faith.