De Sade was only using philosophical hedonism to justify his niche (and pretty childish) erotic writings. Not saying he wasn't a raw badass (that's a taken) but it's hardly serious stuff.
Depends what you mean by serious. He got locked up and tortured for writing it, so someone didn't find it funny!
Depends what you mean by serious. He got locked up and tortured for writing it, so someone didn't find it funny!