Excerpts from my booklet:
There are no exceptions to the eternal moral law. Art is not exempt from the moral law. A particular work may be art and moral, or art and immoral, or moral and not art, or immoral and not art. It is false to assume that, if a work is truly a type of art, then the moral law does not apply, or that any type and degree of immodesty would somehow become moral. The artist must strive to avoid sin in all areas of his life, including in his artwork. Good art is a reflection of the glory of God, and of His Creation, especially humanity. Immoral art offends God and harms humanity.
Sin is nothing else but a knowingly chosen immoral act. Pornographic material is not itself a sin, but it is related to various serious sins. The Catechism of the Catholic Church summarizes the “participants” in the sins of pornography as “actors, vendors, the public.” In other words, those who commit the sins related to pornographic material fall into three categories: (1) those who create pornography, such as actors, performers, photographers, writers, and other persons, (2) those who distribute pornography, such as vendors and other persons, and (3) those who use pornography, such as members of the public. Therefore, the sins related to pornography can be divided into three types: (1) creation, (2) distribution, (3) use.
The use of pornography, even within marriage, is often associated with various sexual sins.
But even apart from particular intrinsically evil sexual acts that may accompany the use of pornography, this usage is also immoral, even when used (viewed, read, etc.) by a married couple. The holy Sacrament of Marriage, or even a merely natural marriage, does not justify any sin.
You will not be able to avoid serious sexual sin, unless you practice all the virtues, in cooperation with grace, every day…. You will not be able to free your life from sin, unless you fill your life with virtue. If you merely learn a list of sins, and try to avoid those acts, you will not be able…. You cannot remove darkness from a room, except by adding light. You cannot remove the darkness of sin from your soul, except by adding the light of virtue.