What is the message behind Marquis de Sade's "120 days of Sodom"?

Many people seem to insinuate this book had a deeper meaning. For example, according to wikipedia Sade's books "challenge perceptions of sexuality, religion, law, age, and gender in ways that de Sade would argue are incompatible with the supernatural". For me this is a bit too vague to even understand, but it sounds like rubbish.

I read this trash, and it seemed to me to be merely a sexual fantasy/fetish of Sade, which he wrote in prison to be able to experience some sexual relief or something. Sade is known to have hired tons of prostitutes (who complained about him torturing them), he had sexual relations with his sister in law. He impisoned and abused "Rose Keller" (hmm.. doesn't that remind you of what happened in this book?). His entire life seems like he is one of the libertines he describes in this book, minus the coprophagia perhaps.

Can anyone explain to me why we haven't totally disregarded this man as a lunatic and his books as his deprived fantasies?

"Evil is rationally self-consistent."

Sade was a horny guy and into S&M games, but I doubt he was a villain in any way. If everything said about him was true, he was an actual villain in his twenties, but he was an upstanding citizen from 1789 onward. a lot of the infamy I suppose was to sell books. He was a far left former Noble writing to expose power structure, and he provided the French revolution with a collection of far left religious texts, which do not mention Christ or God in any positive sense, but draw it from negative space. It's the foundation of noir, of modern villains.

The essence of religion is in rejecting Sade's villains' philosophy when you are put in their shoes, all the rest is corollaries. Religion is not about sex games, it's about evil and power.

Sade is suppresed, so Nietzsche steals his villains' philosophy, and contemptibly, takes it seriously. The Nazis were Sade made real, it was uncanny. From 1945 on, Sade is read, because Nazi type evil made it clear what he was talking about way back when.