Even though the Church pardons sins, she still does not authorize them. Christ Himself gave her the power of pardoning repentant sinners but not to deny the existence of sin. Thank God some sinners acknowledge their sin; there have always been some, and their stories fill the history of the Church.
The new element which the debate on abortion reveals is that at present people deny sin. One denies transgressions of the natural law first, then of the divine law: In declaring good what is evil, man usurps the place of God and substitutes himself for God. Not only does man fail to see and acknowledge the evil he does, but this evil he declares good for him. God's forgiveness offered to man, then, loses its object. Thus by blinding himself to his fault, man closes himself to the salvation God offers him. Is that not perhaps sinning against the Holy Spirit?
It is important to note that, contrary to those who might try to "democratize" it, truth is by definition immutable: It cannot evolve nor change according to the whims of public opinion. The Church therefore must remain loyal to its mission, and abide by the precepts of morality which are based on Divine Law.
CBCP PASTORAL LETTER: "LOVE IS LIFE" (1990)