American culture is super-saturated with pornography and sexual temptations that are destroying our culture. Christianity is counter-cultural in that Jesus taught that to even think about committing adultery or using someone for your sexual gratification is a sinful act. He expects us to control our thoughts, desires and actions. Sexual lust is compared to a fire that must be kept under control and within the boundaries of marriage. If not, it will spread like a wild fire and destroy both one's life and our family members.
The teaching of Jesus on this issue gets right to heart of the problem in that he addresses the intent of the heart of the individual. Even though we may not actually commit the act of adultery, Jesus deals with the real underlying cause which is lust. He considers this a sin and expects us to deal with it constructively with his help. This was quite a revolutionary and counter-cultural message in light of all the rampant sexual behavior dominant within the Roman Empire at that time (and in American culture today).
In light of the current marriage controversy in our culture, the pagans hate the Christian concept of the biblical family unit which is one man and one wife for life. Yet, the traditional family is an essential basic unit of Christian culture. This is because the family plays an essential role in the character formation of Christian youth. The transfer of God's value system from one generation to the next occurs within the family unit. Sexual purity within marriage is essential to maintaining the family bond. God sees adultery as a rebellious and treasonous act with regard to his Kingdom because sexual sin outside of marriage directly attacks the security of the family unit.