Everyone seems agreed that writing about sex is perilous, partly because it threatens to swamp highly individualised characters in a generic, featureless activity (much like coffee-cup dialogue, during which everyone sounds the same), and partly because it feels... tacky.
I do probably come down a little hard on a group of people I call the 'blue chip gays.' I mean people who have managed to become very, very famous and are still very famous partly through staying in the closet, like Jasper Johns, Cy Twombly, Susan Sontag, Harold Brodkey and others.