1859 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 heart (Mt 3:5-6; Lk 16:19-31) do NOT diminish, but rather increase, the voluntary nature of a sin.
(I place the emphasis there because many who have stalked and tormented me think that "oh, what we are doing is not really wrong" or "harden their hearts to be cruel because they think they 'have to be cruel.'" The Catechism points out that both feelings actually worsen, rather than 'mitigate' the commission of mortal sin because there is a deliberateness of thought and of a 'setting to' do the sin. Think of feigned ignorance and hardness of heart as signs of extra premeditation of conducting mortal sin.)
1861 Mortal sin is a radical possibility of human freedom, as is love itself. It results in the loss of charity and the privation of sanctifying grace, that is, of the state of grace. If it is not redeemed by repentance and God's forgiveness, it causes exclusion from Christ's kingdom and the eternal death of hell, for our freedom has the power to make choices for ever, with no turning back. However, although we can judge that an act is in itself a grave offense, we must entrust judgment of persons to the justice and mercy of God.
(I think this is pretty clear. Let me point out the last sentence though. No one has a right to judge what someone else is doing; only God has that right. Here, we are not speaking of the law, for obviously we can identify people breaking the civil law. We are speaking here of someone deciding they can judge someone else's real or perceived sin. For example, those who stalked and photographed my private life when I was not in public ministry, trying to 'catch me in sin' and who disseminated that material have offended against God to his very face. This is true even if I was not the "someone," but any private person cannot be stalked, silently and behind their back accused and judged of sin, and persecuted, because by that you push God out of his chair and do an injustice not only against the secretly stalked but you have also made God your enemy by your presumption. I hope this is very clear to you all).