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I wholeheartedly agree with this, and am female. Surprised?
I think that unless they have previously agreed otherwise before the marriage, men and women do have an obligation to have sex with each other. Not in a "Woman! Sex now!" sort of way, and definitely not out of a feeling of obligation, but people who have radically different ideas about how often they have sex do not belong in a marriage in the first place. It causes too much pain to the one who wants sex but isn't getting it.
Some spouses still love their husband/wife, but just lose interest in sex altogether. Okay, fine, but if that's the case then give your spouse full license to seek sex elsewhere. If you don't care about sex, then it shouldn't bother you if they're getting it from someone else. Sex is a basic human need for the vast majority of us, and denying it to someone while holding them to an agreement of fidelity is simply cruel.
(And yes, this is the "Dan Savage line" on sexless relationships. I think he's got it dead-on)