Several interesting discussions developed in the comments of the post an argument against limbo. One of them revolves around the question of the compatibility of determination to sin with moral responsibility for sin? To what extent can the action of other persons make a given person likely to sin? To what extent can a person be morally responsible for an evil deed if he was practically certain to do it in the first place?
The argument was made that if a person who has a 99% chance of sinning is not held morally responsible for that sin, than a person who has a 99% chance of acting virtuously is also not morally responsible for the virtuous deed, and ultimately, no one is held morally responsible for any good or evil deeds.
There is a long-lasting argument between philosophers over a "compatibilist" or "incompatibilist" understanding of free will and determinism. The former view holds that free will is compatible with the choice's being predetermined (and in principle predictable) in the sequence of causes–even if, all things considered, there was no ultimate possibility that the person would make a different choice, the choice was free because it proceeded from his desires and deliberation–while the latter view holds that free will is incompatible with a predetermination of the choice.
The question of the responsibility for sin given that one is "very likely" to sin and given that one is "certain" to sin are not entirely the same, but are closely related. My first remark on all this is to note that in the philosophical discussions, the difference between good and evil is frequently overlooked or considered to be irrelevant. The question is reduced to a consideration of choosing A or B, and the effect of predictability or determination of the choice upon moral responsibility for that choice. If one is certain or almost certain to choose A, is one responsible for choosing A?
It seems to me fundamentally mistaken to consider the question in abstraction from the question of good and evil, or from the question of whether the action in question fulfills or harms the will's fundamental freedom and orientation.
The question of moral responsibility seems to amount to this: is the human person, as a person, the cause of the good or evil of the choice they make and the act they do? If a person hurts someone else while sleepwalking, the person is the cause of that evil, yet not as a person, since the properly human acts of reason and will are not involved in the act at all. Again, if a parent purchases medicine for a sick child and gives it to that child, unaware that a malicious person has put poison into the medicine bottle, the parent is not morally the cause of the evil of "poisoning the child," because, though they deliberately choose to given the contents of the bottle to their child, and in this sense choose something bad, the reason for the badness of the choice is not in them, but in the person who put the poison in the bottle.
What should we say about a case in which one person leads another person to an evil choice? If parents, for example, persuade their ten year old daughter to kill her child by abortion? In such a case the act proceeds from her reason and will, and in this sense is a free and moral act. However, the question remains: to what is the evil of the act, and the disorder in her reason and will to be attributed? To her, or to her parents? While God alone can judge the heart, I would say that if she was in general well disposed to life and unlikely to make that choice without the influence of her parents, and under the influence of her parents unlikely not to make that choice, then the disorder of the choice is in any case to be principally attributed to her parents, and with high probability not to be attributed to her. For, when we consider her own principle of motion, we see a tendency to good action, which in this particular case is broken, hindered from coming to actuality. Since there is a highly probable explanation of this fact in her parents, it is unreasonable and improbable to attribute the explanation to the girl herself, even though it is in principle possible.
What about when one person leads another person to a good choice? If someone persuades a woman not to have an abortion? To what extent is the goodness of this choice to be attributed to the woman herself? As in the other case, if she was otherwise inclined to have an abortion, yet under the influence of someone else unlikely to have an abortion, then the correctness of the choice can be in some sense principally attributed to the person who persuades her to keep her child. However, if she is persuaded on the basis of a fundamental will for something good (rather than through some kind of trickery), then the goodness of her choice can also be attributed to her. Insofar as she had a particular inclination that would have led her to have an abortion, which was overcome through the intervention of another person, she is not morally responsible for the goodness of her choice, anymore than the girl in the other example is responsible for the badness of her choice. But insofar as the good choice comes from a more fundamental inclination of her will to good, she is responsible for its goodness, and praiseworthy for it.