I don't think all guys demand it. But men just NEED sex more than women do IMO. Maybe when you find the guy that wants it, but doesn't demand it - that's the guy for you?!? Good luck
aham3, has answered your question. Such men would expect you to indulge their corruption because sensual desire inflames them to immoral excess. They are brazen fornicators.
A follower of Christ would know your body is a temple of the living God; bought with a price to glorify God in your body and spirit. A man of God would have no want to defile your body or their own because the pleasures of sin have nothing on the hope of the promise and unsurpassed inheritance through Jesus Christ.
Men are kept more aware of the pleasures of sex, and face fewer practical consequences -- especially in modern society, where it is increasingly common to see single mothers who have never been married, and where people at all levels of society have demonstrated a willingness to rationalize their behavior by defining sexual acts as "not sex."
Also, as Ryan Reynolds' character so pungently pointed out in "Definitely, Maybe", there still is no boy word for "s**t".
So the reality is that men ask for extra-marital sex for the same reason they ask for large helpings on dessert -- they enjoy it and feel no shame in trying to get as much as they can.