Jesus' first message is ‘The time is fulfilled, and the kingdom of God has come near; repent, and believe in the good news.’ (Mk 1). He warns that those who ignore His words are building on the sand, and their house will fall (Mt 7) and his final instruction to his disciples is to 'make disciples of all nations... teaching them to obey everything that I have commanded you. (Mt 28). God is the king of the universe: He decides what is right and wrong, and arguing the toss with Him is truly a waste of time.

In that context Paul warns us that: 'Do not be deceived! Fornicators, idolaters, adulterers... thieves, the greedy, drunkards, revilers, robbers — none of these will inherit the kingdom of God.' and carries on in the same passage 'Shun fornication! Every sin that a person commits is outside the body; but the fornicator sins against the body itself. Or do you not know that your body is a temple of the Holy Spirit within you, which you have from God, and that you are not your own? For you were bought with a price; therefore glorify God in your body.' (1 Cor 6)

Similarly it is clear that the early church rejected all forms of sexual activity outside marriage; any attempt therefore to claim to be a Christian when choosing to have sex outside marriage makes no sense unless 'Christian' is to be reduced to no meaning whatsoever. Instead we are in danger of being like Eve and believing the lie of Satan, that God was depriving her of something good for no good reason.