Although I don't like BDSM theme and de Sade in particular. Don't think there is any "pholosophy" beyond his books.
de Sade is, uh... A unique one? A lot of his libertine views on sexuality are quite disturbed, I think, and not necessarily indicative of "proper" BDSM. A lot of very graphic depictions of pedophilia and rape, whereas the BDSM scene as I've understood it is heavily based on clear consent and at no point has any relation to those two things.
More "torture porn" than genuine porn, I think.