Christians are followers of Christ. They live not of the flesh but in spirit even though they live in this world. They can do all things through Christ who strengthens them and the word of God is their daily bread. These are a few of the many characteristics of a Christian. So in my opinion, Christians can't and shouldn't fornicate as the Bible said that "flee from fornication " and if by weakness of the flesh we do it, we should repent and not make excuses to justify our sins. It's really not right for a christian to fornicate and not regret his/her actions . God help us all!