The question was put: "How sacred is secular marriage on a scale of 1 to 10?"
To which I responded:
A simple number from 1 to 10 would not do justice to my opinion. Is the question about how sacred secular marriage is to God, to me, or to the married couple? Also, you have not given an adequate definition of "secular marriage". Is it defined as any marriage "for time"? Or is it defined as a marriage between two non-believers who are simply getting married because they want to live together and take advantage of the legal benefits associated with marriage?
So the best answer I can give is this:
In my opinion, sex tends to be inherently sacred, although its expression has many moods other than reverence, including passion, exuberance, obsession, longing, pleasure, compassion, and fear. Marriage would probably not exist if there were no sex, although most marital relationships have many more layers than just the sexual relationship. I believe that God does command us to be wise in the sharing of our sexuality, because there is natural happiness to be gained, and misery to be avoided, by exercising reasonable control over our sexual expression. Sex is sacred not only because of the joy and pleasure it brings, but also because it should be treated with a certain amount of caution and circumspection, and not subjected to capricious flames of irresponsible passion. How sacred a marriage is for the couple will depend on how they as individuals subjectively feel and act about it.