but the explanation for *why* it is offensive that legsdiamond gave (and that I have heard from others, to be fair) is the part that smells like BS to me... the idea that people are genuinely hurt that other people are not turned on by the image of them making love.

Unless you're a professional porn star or actor, chances are that the sight of you personally making love IS pretty "ewwwwww" anyway... and most people know that too, I think.