Some paragraphs from the Catechism of the Catholic Church on ignorance as a sin and ignorance that diminishes the guilt of sin:
scborromeo.org/ccc.htm
[1735](javascript
penWindow(‘cr/1735.htm’)
Imputability and responsibility for an action can be diminished or even nullified by ignorance, inadvertence, duress, fear, habit, inordinate attachments, and other psychological or social factors.
[1736](javascript
penWindow(‘cr/1736.htm’)
Every act directly willed is imputable to its author … An action can be indirectly voluntary when it results from negligence regarding something one should have known or done: for example, an accident arising from ignorance of traffic laws.
1790 A human being must always obey the certain judgment of his conscience. If he were deliberately to act against it, he would condemn himself. Yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed.
[1791](javascript
penWindow(‘cr/1791.htm’)
This ignorance can often be imputed to personal responsibility. This is the case when a man "takes little trouble to find out what is true and good, or when conscience is by degrees almost blinded through the habit of committing sin."59 In such cases, the person is culpable for the evil he commits.
[1792](javascript
penWindow(‘cr/1792.htm’)
Ignorance of Christ and his Gospel, bad example given by others, enslavement to one’s passions, assertion of a mistaken notion of autonomy of conscience, rejection of the Church’s authority and her teaching, lack of conversion and of charity: these can be at the source of errors of judgment in moral conduct.
[1793](javascript
penWindow(‘cr/1793.htm’)
If - on the contrary - the ignorance is invincible, or the moral subject is not responsible for his erroneous judgment, the evil committed by the person cannot be imputed to him. It remains no less an evil, a privation, a disorder. One must therefore work to correct the errors of moral conscience.
1801 Conscience can remain in ignorance or make erroneous judgments. Such ignorance and errors are not always free of guilt.
[1859](javascript
penWindow(‘cr/1859.htm’)
Mortal sin requires full knowledge and complete consent. It presupposes knowledge of the sinful character of the act, of its opposition to God’s law. It also implies a consent sufficiently deliberate to be a personal choice. Feigned ignorance and hardness of heart133 do not diminish, but rather increase, the voluntary character of a sin.
[1860](javascript
penWindow(‘cr/1860.htm’)
Unintentional ignorance can diminish or even remove the imputability of a grave offense. But no one is deemed to be ignorant of the principles of the moral law, which are written in the conscience of every man. The promptings of feelings and passions can also diminish the voluntary and free character of the offense, as can external pressures or pathological disorders. Sin committed through malice, by deliberate choice of evil, is the gravest.