"But my question is, why? Yes, we know what Jesus said in Matthew 5:28, but the word He used there was "adultery" not "fornication"
(NIV)
1 Corinthians 6:18 "Flee from sexual immorality. All other sins a person commits are outside the body, but whoever sins sexually, sins against their own body."
(King James)
1 Corinthians 6:18 "Flee fornication. Every sin that a man doeth is without the body; but he that committeth fornication sinneth against his own body."
Therefore we should not committeth thou sin against thy Lord thy God.
Matthew 5:28 "But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart."
The problem with inappropriate content is when you look at it, you are looking at the inappropriate content lustfully.
Lust by dictionary.com
1. intense sexual desire or appetite.
2. uncontrolled or illicit sexual desire or appetite; lecherousness.
3. a passionate or overmastering desire or craving (usually followed by for ): a lust for power.
Matthew 7:16 "By their fruit you will recognize them. Do people pick grapes from thornbushes, or figs from thistles?"
Proverbs 5:5 "Her feet go down to death; her steps lead straight to the grave."
For example lets say at first someone is simply wanting to have sexual relief so they stimulate themselves, next they may be enticed to look at inappropriate content, pretty soon you have a full blown addiction.
Why is this bad? Because pretty soon you will have to give more and more of yourself and the inappropriate content won't satisfy you anymore. You will want to start going to a hooker or other terrible things. Lustful movies, rape, sexual immorality.
Hebrews 4:15 "For we do not have a high priest who cannot sympathize with our weaknesses, but One who has been tempted in all things as we are, yet without sin."
Jesus was flesh and blood, Jesus is not looking down on you from some ivory tower shouting "You must resist temptation!" Jesus has been there and done that and yet was without sin.
The problem with this is you may be compromising your beautiful walk with God, you think you have to be single and look at inappropriate content but why not just wait til you get married if you have such a passion? It is like a fire, if you feed the fire it will grow bigger, if you stop feeding it then it will go out.
You may feel like your gonna explode because of build up but that is only if you keep giving in to lustful thoughts. It all starts with your thought life. When you gave your life to Christ you had gotten a new heart, but you still have the sin nature to deal with.
So you have a sin nature not a sinful heart,
Romans 7:22 "For in my inner being I delight in God's law;"
Also
James 2:10 "For whoever keeps the whole law and yet stumbles at just one point is guilty of breaking all of it."
Romans 2:25 "Circumcision has value if you observe the law, but if you break the law, you have become as though you had not been circumcised."
1 Corinthians 7:19 "Circumcision is nothing and uncircumcision is nothing. Keeping God's commands is what counts."
And having a wife may help you with that
Proverbs 18:22 "He who finds a wife finds what is good and receives favor from the LORD."
If you had a wife for life then when you had trouble she could comfort you and give you emotional and mental support and then you could become one with her
1 Corinthians 6:16 "Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, "The two will become one flesh."
Paul said it was better to marry because of so much immorality going on, each man should have his wife and each woman should have her own husband.
1 Corinthians 7:5 "Do not deprive each other except by mutual consent and for a time, so that you may devote yourselves to prayer. Then come together again so that Satan will not tempt you because of your lack of self-control."
I am not lying, we all sin that is why we need to ask God for forgiveness but look deep into your heart, it is wrong to look at inappropriate content and if it goes unchecked it will become worse and degenerate.
That is how all sin is
Romans 7:24 "What a wretched man I am! Who will rescue me from this body of death?"
Jesus will!
Romans 10:13 "for, "Everyone who calls on the name of the Lord will be saved."