SSMGuy, your analogy is a useful one. It's hard for a man who wants sex, especially after years of longing and desperation, to really, truly put himself in the shoes of someone who just doesn't feel the desire. I know I always thought, and later said, "If it means everything to me, and nothing to you, then I don't see why you haven't tried to just go through the motions and get it over with."
Of course, the truth is that going through the motions to get it over with can help you get started, but it's not a solution, because we are not going to be satisfied with just that for long. And of course, as you describe, sex is messy and weird from a completely objective point of view.
One caution, though: your analogy does miss one important positive and one important negative factor in most SS marriages.
On the positive side, it would be more accurate if your hypothetical husband used to enjoy the mud baths with his wife, and the mud baths were a big part of the reason they got together in the first place. To make the analogy to sex better, he would have to have fond memories of those old days in the mud bath, even if he currently feels no desire to get into one. The LD partner usually has a sexual past with the HD partner that's different than their current situation.
On the negative side, there would also have to be overwhelming societal pressure to have a satisfying mud life. Our hero, who has lost his desire to squish in the mud with his wife, should have to hear about the joys of the mud baths from TV, movies, radio, print, advertising . . . there should be shelves full of self-help books purporting to teach people how to make their mud lives more satisfying or make their mud-squishing more fulfilling for the others in the mud.
And there should certainly be a constant stream of myths and "conventional wisdom" about mud and mud baths that confuse the hell out of everyone involved.
