I believe the family is a structure designed by God. Within the family, God intended one man and one women to make a lifetime commitment to one another. These two may become parents and then have the sacred responsibility of raising their children.
Now that I have made the basic statement let me elaborate on it a bit at a time.
God designed the family just as He designed everything else which exists. He has intentions on how the family is supposed to work, and for humans to give the definition of family a makeover is sin. He has the right to be Lord over the family as He has the right to be Lord over all of Creation. This includes bringing judgment at His discretion.
Marriage, the relationship which begins a new family is designed by God and His intentions for it are for one man to be married to one woman. I fully understand the Scriptures include many cases of polygamy. (They also have cases of murder, rape, incest and other deplorable actions we would not endorse.) I believe the nature of people indicates we are intended to have one other marital partner of the opposite gender. We are designed in such a way to desire such an exclusive relationship.
Parenthood is a part of most families and should be taken on as a responsibility to God, society and the children themselves. The possibility of creating children in situations which are not conducive to the child’s welfare, is one of the main reasons sexual relationships outside of marriage are sin. Children exposed to the wrong things too early, especially sexuality, will be adversely affected by that loss of innocence, and parents should take protecting their children from this loss of innocence as a personal responsibility. Children who are not disciplined in regard to their behavior will also face challenges which may well limit their potential for the rest of their lives. These kids often become adults who harm society and cannot understand the need to be in submission to any authority, earthly or eternal.