A person viewing porn is not a participant in what they are looking at but they are nonetheless guilty of sin.
Pornography is the recording of (often illicit) sexual images for the purpose of sexual stimulation. Looking at pornography isn't sin because "there's no good reason to do it," right? Looking at pornographic images is sin because, among other things, doing so involves unbridled lust, covetousness, adultery, deep selfishness, and the perversion of God's intended design for human sexuality. At bottom, as with all sin, the sin of looking at porn is, for the Christian, a twofold thing:
1.) Denying who they are in Christ. (Self-deception.)
2.) Standing in God's place in their life. (Rebellion, pride, self-will.)
These are the two things that stand at the heart of all of a Christian's sin. Porn addiction, uncontrolled temper, laziness, neurotic fearfulness, greediness, pride, and so on, are all just the results of a Christian doing these two things.
The Church in some instances does speak out forcefully against porn. But, as others have observed in this thread, there is as much addiction to porn within the Church as without it. This is so, I believe, primarily for the following reasons:
1.) No proper discipleship.
2.) The Church is no longer holy and separate.
3.) Spiritually-juvenile teaching ("a mile-wide but an inch deep").
4.) Ignorance of the Bible.
One need not be addicted to porn to be guilty of sin. Simply looking at it with the intent of sexual self-stimulation/gratification is sufficient to make it sinful. (Matthew 5:28; Philippians 4:8; Ephesians 5:1-13)
Salvation brings a person into relationship with God, but it is fellowship with Him (1 John 1:3; 2 Corinthians 13:14; Revelation 3:20) that brings a person free of the grip of Self and sin. Put another way: The shed blood of Christ cleanses us from the stain and penalty of our sin but it is the cross that frees us from its power (Romans 6:1-11; Galatians 2:20; Galatians 5:24; Colossians 3:1-4). Too few Christians today have any idea what this means. And so, they are caught in all sorts of sin, not just porn addiction. There really is, though, "a way of escape" from any and all sin. Paul describes this "way of escape" in detail, particularly Romans 6 and Romans 8:1-16. This "escape route" isn't focused on particular sins but on the root and ultimate source of them all: The "old man" in control. It rests upon "walking in the Spirit" which is something that most Christians know nothing of though it is basic to Christian living (Galatians 5:16, 25) and living free of bondage to sin.
Though there are myriad psychological methods to dealing with addiction to porn, God's way to freedom from such an addiction is the same way to freedom from all sin:
By the word of Truth:
Hebrews 4:12
12 For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit, of joints and of marrow, and discerning the thoughts and intentions of the heart.
Psalm 119:9-11
9 How can a young man keep his way pure? By guarding it according to your word.
10 With my whole heart I seek you; let me not wander from your commandments!
11 I have stored up your word in my heart, that I might not sin against you.
Matthew 4:1-4
1 Then Jesus was led up by the Spirit into the wilderness to be tempted by the devil.
2 And after fasting forty days and forty nights, he was hungry.
3 And the tempter came and said to him, “If you are the Son of God, command these stones to become loaves of bread.”
4 But he answered, “It is written, “‘Man shall not live by bread alone, but by every word that comes from the mouth of God.’”
2 Peter 1:3-4
3 His divine power has granted to us all things that pertain to life and godliness, through the knowledge of him who called us to his own glory and excellence,
4 by which he has granted to us his precious and very great promises, so that through them you may become partakers of the divine nature, having escaped from the corruption that is in the world because of sinful desire.
By the Power of God:
Galatians 5:16
16 But I say, walk by the Spirit, and you will not gratify the desires of the flesh.
Philippians 2:13
13 for it is God who works in you, both to will and to work for his good pleasure.
Romans 8:13-14
13 For if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body, you will live.
14 For all who are led by the Spirit of God are sons of God.
Ephesians 3:14-16
14 For this reason I bow my knees before the Father,
15 from whom every family in heaven and on earth is named,
16 that according to the riches of his glory he may grant you to be strengthened with power through his Spirit in your inner being,
By the Armor of Righteousness:
Romans 13:12-14
12 The night is far gone; the day is at hand. So then let us cast off the works of darkness and put on the armor of light.
13 Let us walk properly as in the daytime, not in orgies and drunkenness, not in sexual immorality and sensuality, not in quarreling and jealousy.
14 But put on the Lord Jesus Christ, and make no provision for the flesh, to gratify its desires.
1 John 1:9
9 If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
Ephesians 5:7-12
7 Therefore do not become partners with them;
8 for at one time you were darkness, but now you are light in the Lord. Walk as children of light
9 (for the fruit of light is found in all that is good and right and true),
10 and try to discern what is pleasing to the Lord.
11 Take no part in the unfruitful works of darkness, but instead expose them.
12 For it is shameful even to speak of the things that they do in secret.
1 Peter 1:15-16
15 but as he who called you is holy, you also be holy in all your conduct,
16 since it is written, “You shall be holy, for I am holy.”
Good questions, all. See above.
James 2:10
10 For whoever keeps the whole law and yet stumbles in one point, he has become guilty of all.
God is clear that it IS sin. It matters not, then, what the individual sinner may think about it. God will judge and punish their sin whether they call it sin or not.
No.
Absolutely not.
It doesn't matter what sinners want to "reason" about their sin. What matters is what God thinks and has said.