Catholic Doctrine condemns Sex outside Marriage as sacrilege against the sacrament of marriage

Concerns about diseases and sexual justice and the meaning of sex aside, the Catholic Church sees sex outside wedlock as saying no to God's gift of marriage and God's sacramental help to make marriage a success.

The Roman Catholic Church teaches that there are seven sacraments. A sacrament is a symbolic rite that puts power from God into you that makes you pleasing to him and fit for being with him forever in Heaven. Marriage is thought to be one of these sacraments. So marriage is believed to make the love of husband and wife holy. The Roman Catholic, Preface of Marriage III says, "The love of man and woman is made holy in the sacrament of marriage, and becomes the mirror of your everlasting love". So marriage makes love holy. Sexual love outside marriage then is not holy. If we deny this, then we deny that the Church is right about the sacraments and that the Church has any monopoly on discerning the truth and indeed that the Church is worth believing in. We are affirming that we can get to Heaven without it.

The Bible says at 1 John 2:9-10 says that the man who hates his brother in Christ is in darkness and has his eyes blinded and doesn't see where he is going. This implies that there is no light in him at all only darkness and evil. Christians are not allowed to think of such a man as good in any way.

1 John 3:15 says that anybody who hates his brother is a murderer and eternal life dwells in no murderer's heart. This means that simply hating somebody makes you as bad as a murderer inside and that no murderer will have eternal life so it is a very serious sin. This parallels Jesus' saying that whoever looks at a woman with desire commits adultery with her in his heart or thoughts as some translations put it (Matthew 5:28). Neither verse indicates that they are thinking of people who are planning to do anything. They are speaking of people who would murder and commit adultery if they got the chance and could get away with it. Jesus sees the desire to have sex with a woman as adultery even if you or she are not married because for him fornication and adultery are the same sin under different names.

The sin he is against is sex outside marriage which can take the form of fornication or adultery. So he can say that an unmarried pair having sex is still adultery. He said that whoever divorces his wife forces her to commit adultery (Matthew 5:32). The man can't say that his wife makes her own decisions once she leaves. When he gives her a divorce he is trying to force her to commit adultery by giving her the freedom to wed again. He sins in making an adulteress of her. If he does that just by divorcing her, then how much more is it a sin to simply think of having sex or to have sexual fantasies? Obviously all this implies that sex outside marriage is a grave sin. It is so bad that you cannot have ANYTHING to do with it or enabling anybody to consider it at all!

New International Version, 1 Corinthians 6:12-17

“I have the right to do anything,” you say—but not everything is beneficial. “I have the right to do anything”—but I will not be mastered by anything. You say, “Food for the stomach and the stomach for food, and God will destroy them both.” The body, however, is not meant for sexual immorality but for the Lord, and the Lord for the body. By his power God raised the Lord from the dead, and he will raise us also. Do you not know that your bodies are members of Christ himself? Shall I then take the members of Christ and unite them with a prostitute? Never! 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.” But whoever is united with the Lord is one with him in spirit. Flee from sexual immorality. All other sins a person commits are outside the body, but whoever sins sexually, sins against their own body. Do you not know that your bodies are temples of the Holy Spirit, who is in you, whom you have received from God? You are not your own; you were bought at a price. Therefore honor God with your bodies."

The Church makes sure the above reading from St Paul where God supposedly inspired him to say that sex outside marriage is sinning against your body is read at Masses. Paul claimed that this sin is the only sin against your body. He said it is terrible because Jesus bought your body and it belongs to God. This can only be understood as saying that sex outside marriage is bad just because Jesus said it is. He bought your body thus he decides that you must not have sex outside marriage. It is not right to judge somebody as breaking God's law when there is no proof that there is a God and that it is his law. There is enough to judge people about. Faith should never risk making life harder for others.

Paul is clear that sex outside marriage is a sacrilegious attack on Jesus. He rejects the notion that the chief consideration is any harm or possible harm to the participants. It is devaluing – it’s a heart issue. It devalues Jesus. It is a clear denial that harm is enough to make something immoral.  That is why we should include straight people who have sex outside marriage as having the need to be protected like LGBT plus who have sex.  Opponents are just bigots.