Do you see sex like this? http://tinyurl.com/n4d4zd
We live in a culture where sex is not so much an act as a thing: a substance that can be given, bought, sold, or stolen, that has a value and a supply-and-demand curve. In this "commodity model," sex is like a ticket; women have it and men try to get it. Women may give it away or may trade it for something valuable, but either way it's a transaction. This puts women in the position of seller, but also guardian or gatekeeper … Women are guardians of the tickets, men apply for access to them. This model pervades casual conversation about sex: Women "give it up." men "get some."
The commodity model is shared by both the libertines and the prudes of our patriarchy. To the libertine, guys want to maximize their take of tickets. The prudes want women to keep the tickets to buy something really "important": the spouse, provider, protector.