The thing to remember about de Sade is how to read him. Although he was certainly involved in and indulged various
unusual sexual practices, his writing is not so much aimed encouraging the
Libertine attitude he so often seems to
espouse, but rather is better viewed as an
experiment upon the state of mind of the reader.
Try reading La Nouvelle Justine or 120 Days of Sodom and noting the affects upon yourself as you read, not just the minor physiological effects related to arousal and disgust but also the more complex sense of quiet emptiness you get as you read further. The shocking while at the same time inevitable conclusion of Sodom for example, induces more thoughts on the nature of sin and the indifference of the Universe than almost any other book I've read.
de Sade was a truly revolutionary writer and whatever the circumstances of his private life should be regarded as that alone by following generations. The evidence for his proclivities as purely mental is clear from his refusal to execute any prisoners during his time as a Justice of the Revolution. The cheapening of his memory and work with bland powerplay sex and the frankly pathetic mores of modern sadomasochists are regrettable and detract from his deserved fame as one of the most thought provoking artists of the modern age.