That's how we view sex, acceptable sex, that is. For there is more than one way to have sex, yet we don't really like the idea. But why is that?
If one can be married without having sex, but one cannot have sex without being married, sex must be more important than marriage. And if that's the case, wouldn't it be better to marry as quickly as possible, try it out and then divorce if the whole thing fails, and marry someone else? That way, sex would be comfortably confined within the context of marriage, and everyone's happy.
But then there is the question of children, for sex does produce children. And children are one of the reasons why sex before marriage is frowned upon, for we consider children born outside of marriage "illegitimate." It's the same language that is evoked in the case of "illegal" immigrants: you have to born to the right parents to be accepted as a human being.
And this brings us back to the idea of one man and one woman, a wedding, and a closed door. This idea that sex belongs to marriage has really to do with property, for a child born out of wedlock has no right to inherit. And this has profound implications to our society as a whole, for if only legitimate children are allowed to inherit, and by necessity there will only be a few, the estates will remain in the family, from father to son. This prevents the re-distribution of property, and ensures the wealth of the families who have been able to amass them, which is why the feudal system endured so long and was so difficult to end.
Now, someone may point to the Jewish system of re-distributing the land every 50 years at the Jubilee as proof that one can have a one man one woman marriage and still prevent a feudalistic system from being created. And in theory this is true, but Israel approved also of polygamy, which brings us to the next point - why can a man have several wives, but a woman not several husbands? Yet, again the answer is found in the procreation department: a woman knows her own child, but a man doesn't. So, again, sex must be restricted to marriage to allow the man to know he is truly the father of the child he calls his own - unless his wife has been unfaithful, in which case there is no knowing, but that's where the restrictions of movement come in, and the modesty requirements, and the whole host of other shaming tactics to ensure the fidelity of married women.
But let's consider for a moment what would happen to our sexual mores if we didn't insist on the legitimacy of the children, if we were happy to raise any child that we found ourselves parenting, and if property was shared equally between men and women? And what if we saw sex as an expression of love instead of ownership? Would it change how we see ourselves and others?
Sex as love instead of ownership has implications that reach to all parts of society, for it recognizes that a relationship doesn't begin at the altar, nor is it guaranteed to last forever; property cannot leave, but people can. Sex as love recognizes also that not all marriages produce children, and not all children live to old age. If we insist that sex must be confined to marriage because of the possibility of procreation, we forget that sex is really more about recreation, and children are the blessing that follows. Sex is what glues a couple together, not the wedding. And in the case of a couple having a child before the wedding and then deciding not the sign the legal contract, is there not enough love in this world to welcome a child? And when it comes to the finances, that's why we have paid maternity leave - or should have it. No child should need to feel that his or her lot in life is different because of his/her parent's choices. Isn't that what we tell adopted children?
In the end it is patriarchy that insists that sex should be confined to marriage, for patriarchy views sex as a means of conquest in which the man subjects the woman to his own will, and considers her body as a vessel, designed only to produce legitimate heirs. The woman doesn't exist as a person with rights, for she can neither consent to sex before the wedding, nor withhold consent after the wedding. She becomes a non-person, whose only role in life is to be a mother and a wife, and ensure that the property, which she doesn't own, is handed over to the rightful owners; 1 % of the world's land is owned by women, the rest belongs to men.
Now, I can already hear my egalitarian sisters and brothers say that there is a better way. Mutual submission, love and respect, can transform a marriage from ownership to love. And this is very true. But do egalitarians accept children born out of wedlock? Do they support a redistribution of the land that would allow women equal ownership of the land and decision making? Or is this just another way to say, "We want equality without challenging patriarchy." King Solomon had a thousand wives; we don't squirm when we read about it. But if the neighbor has her boyfriend move in, we consider her to have lost all her morals. And this happens because we can only see a woman from the perspective of her body: who has access to it, who doesn't. A "good" girl protects her purity until the day she becomes the property of a man, and therefore a legitimate mother of legitimate children. Women who, with or without their consent, have lost their purity carry the consequences and the shame of the entire patriarchal society that prides in honor; the honor of punishing those who don't comply.
Our sexual mores aren't confined to how we view marriage, they affect every aspect of our lives. Do we want to see women as humans, persons with rights, or objects to be handed over because their bodies are worth more than their minds? This is what we are really talking about when we talk about sex.