I'm not so sure there's a distinction between "pure" hedonism which only hurts oneself/consenting partners/simulations and hedonism in general. Slaanesh isn't the God of Icky-Stuff-We-Wouldn't-Do, or even really the God of Illicit Pleasure, but the God of Pleasure in general. The fact that his cultists and those he corrupts hurt others is because they don't care about anything but their own pleasure, so they'll do anything for a thrill no matter who it hurts.
There *IS* a distinction between hedonism and degradation. Between something you enjoy because it makes you feel good, and something you enjoy because it makes others feel bad.

Slaanesh is sadistic.
Does the innocent joy of a child empower Slaanesh? Does pride in a job well done, or a friend? How about the satisfaction that comes from spiritual wholeness or worship of the god emperor? I would say the indications are that none of them do. That Slaanesh is the prince of sadistic pleasure. Of degrading pleasure. Of pleasure carved from the joy of others. Otherwise, why does he encourage that behavior in his worshippers? If he gains from pleasure in all of its forms, why is he constantly pushing them into self destructive behaviour that lessens the pleasure of others? Unlike every other Chaos god, pleasure is not a self destructive emotion in and of itself. Bloodlust, sickness and change can't exist in stasis. Pleasure can. Sadism fits into the scheme of chaos much more neatly.

Remember, Slaanesh is the weakest of the Chaos gods. By a distinct margin. And yet you're claiming he feeds on by far the widest spectrum of emotion.

Again, I'll quote Black Crusade
Quote Originally Posted by Black Crusade pp 16
Slaanesh represents ... the yearning for luxury and hedonistic over-indulgence, the exercise of cruel and unnatural passions, the pursuit of forbidden vices and unspeakable carnality. The Pleasure Lord always holds open the thrilling promise of the forbidden and the exotic beyond the boundaries of moral and societal lores.
None of which is really the Culture mainstream... Maybe over-indulgence? Maybe? It's hard to say something is over-indulgence when it doesn't really have a cost, doesn't make other people worse off.