Right, from the Catechism of the Catholic Church…
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 do not diminish, but rather increase, the voluntary character of a sin.
But do not forget, illegally downloading music is theft and theft is a violation of the 7th commandment, which is grave matter.
2450 “You shall not steal” (Ex 20:15; Deut 5:19). “Neither thieves, nor the greedy . . ., nor robbers will inherit the kingdom of God” (1 Cor 6:10).
2451 The seventh commandment enjoins the practice of justice and charity in the administration of earthly goods and the fruits of men’s labor.
2452 The goods of creation are destined for the entire human race. The right to private property does not abolish the universal destination of goods.
2453 The seventh commandment forbids theft. Theft is the usurpation of another’s goods against the reasonable will of the owner.
Now you can, as paragraph 1859 says, “Feigned ignorance and hardness of heart do not diminish, but rather increase, the voluntary character of a sin.”
Which seems to be the game you want to play, it is also called moral relativism, which goes against the Church’s Teachings, but it makes it even worse as it increases the voluntary character of the sin, which means it fulfills all three…
*]Full Knowledge: You know it is theft
*]Full Consent: You are chosing to do so
*]Grave Matter: It violates the 7th Commandment
The only way around this is to someone get by Full Knowledge as you say in your post but today for someone to claim that with the RIAA and all the news about the RIAA sueing individuals and Universities actually making it so such software that is used to steal music does not work through their networks, and the curriculum at our High Schools today (I am a teacher at a Catholic Highschool in the Career and Technology Department) there is no way that the average person can not know that downloading copyrighted music is illegal except for through “feigned ignorance” or “hardness of heart”.