I asked the Dalai Lama a couple weeks ago what he thought about sex. He didn't answer my question. Neither did my Buddhism professor in college when I asked him...in fact, he yelled me out of his office. The question remains, however: how does one reconcile the craving inherent in sexual desire with the teachings of Buddha, who says that the root of all suffering is desire?
Augustine had similar problems with reconciling purity of heart with sexual desire: for a man at least, the cultivation of sexual desire involves nurturing the seeds of lust until they become full-blown. At muturity, lust looks for a home, the satiation of its overwhelming desire. One cannot have sex without lust--the grasping after sensual pleasure--and it was this that Augustine had a problem with.
When a man gains control over his body he becomes like a fisherman who is able to catch fish with his hands. In ancient times knights were sometimes forbidden to sleep with their wives before battle since P.E.D. (Post Ejaculatory Depression, a term I was recently enlightened to by a friend) causes sloth and dulls aggression; the mind must be alert to fight.
It's not so much that having dulls the mind; rather, it is that a lack of sex (and the ensuing accumulation of sperm and testosterone) hones attention and allows one to shift energy from one chakra (muladhara-root) to another. Orgasm is a tremendous outflux of energy. When desire is sated, thoughts of sex (again, for men) virtually disappear...for a time. As lost sperm is replenished, sexual energy and aggression commensurates.
But if sperm never leaves the body (not willingly, at least), the tremendous energy seated in the root chakra pools, and it can be channeled upwards toward the head (sahasrara) chakra. Sometimes the energy can be so forceful, you can literally feel it pushing against the insides of your abdomen, trying to get out. The practice then becomes a force of will--keeping sexual desire in check for the benefit of ascetic training takes a great deal of concentration. Desire works like a storm cloud rolling in, letting loose, then retreating, for a time. Some of the most fruitful meditations I have had have been when I was the most charged up sexually, especially at Suan Mokkh, where all manner of sex was strictly forbidden.
Meditating while in the company of mosquitoes has also proved to be good practice. When bitten, the desire to scratch a bite is almost maddening. But if one scratches it, it only gets worse; as long as one gives in to the desire, the bite will never go away. And so gritting one's teethj and refraining action while mosquitos suck themselves stupid, falling bloated to the ground, victims of their own desire, the mind soon learns that the desire to scratch an itch does not last forever, and if left alone, will pass away like a spectre in the night.