Amoris Laetitia: Misquoting St. Thomas on Irregular Relationships?

There is an interesting quote from St. Thomas in the new exhortation Amoris Laetitia.  Unless I am mistaken, it follows the trend of much neo-Modernist "scholarship" by misquoting St. Thomas in favor of a political or religious goal.  Thomas discusses the difficulty that some saints have in spite of their virtuous habits.  It seems to be used in the exhortation as evidence that those who commit reproductive acts in irregular situations might not be guilty of mortal sin.  I have no idea what sort of argument or interpretation might cause one to interpret Thomas's comments in favor of this view.  Apart from what the document actually says, there seems to be an egregious misuse of St. Thomas. 

Here is the passage:

 For an adequate understanding of the possibility and need of special discernment in certain “irregular” situations, one thing must always be taken into account, lest anyone think that the demands of the Gospel are in any way being compromised. The Church possesses a solid body of reflection concerning mitigating factors and situations. Hence it is can no longer simply be said that all those in any “irregular” situation are living in a state of mortal sin and are deprived of sanctifying grace. More is involved here than mere ignorance of the rule. A subject may know full well the rule, yet have great difficulty in understanding “its inherent values”,339 or be in a concrete situation which does not allow him or her to act differently and decide otherwise without further sin. As the Synod Fathers put it, “factors may exist which limit the ability to make a decision”.340 Saint Thomas Aquinas himself recognized that someone may possess grace and charity, yet not be able to exercise any one of the virtues well;341 in other words, although someone may possess all the infused moral virtues, he does not clearly manifest the existence of one of them, because the outward practice of that virtue is rendered difficult: “Certain saints are said not to possess certain virtues, in so far as they experience difficulty in the acts of those virtues, even though they have the habits of all the virtues”.342

 341 Cf. Summa Theologiae I-II, q. 65, art. 3 ad 2; De Malo, q. 2, art. 2.

342 Ibid., ad 3.

The quotes from St. Thomas have nothing to do with the issue under discussion, and seem to be merely manipulated to support a very different position.   Apart from any religious reservations a believer might have about the paragraph, Thomists should be very worried about the misuse of Thomas's texts for political and religious reasons.

I am willing to believe or at least accept anything in such documents that is not obviously wrong.  But the use of St. Thomas in this passage is embarrassing.  Or am I missing something?

ADDITIONAL BUT ONLY PARTLY RELATED COMMENT

Incidentally, is this document claiming that Christians can be sometimes be free of guilt on account of invincible ignorance of the Ten Commandments?  I have seen this in some recent preaching and writers, but not so clearly in other official documents, and never (or almost never) before the twentieth century.     There is an isolated passage from St. Thomas that some have argued proves that there can be invincible ignorance of fornication (De Malo, q. 3, art. 8).  But here he has not yet described the different kinds of voluntary and involuntary ignorance, and is merely distinguishing between ignorance concerning the deformity of the act (such as ignorance that fornication is a sin), and ignorance of the circumstances, (such as that someone is not one's wife).  Interpreting this article as in favor of invincible ignorance of fornication at least seems to conflict with other passages such as:  De Veritate, q. 17, art. 3; l I-II, q. 6, art. 8; I-II, q. 19, art. 5-6;  I-II, q. 77, art. 7, ad 2. But the exhortation seems to be stretching this invincible ignorance to Catholics, and to adultery.