There are two things I place under the value category of Purity, as I'm pretty sure they're facets of the the same thing. The first type is what you might call "irreverence": it's deplorable to indulge in the midst of evil. For example, my conscience has always objected to me slouching or eating candy in a solemn context, like after watching another police brutality video). And I know everyone else shares that feeling. The repugnance to irreverence is extremely strong even though it's difficult to explain. And everyone objects to me that this is just an emotional association. But I think that's exactly the point: being irreverent at times like that degrades, to you, what you should care about. The emotional association is not cultural; it's intrinsic.
The other subcategory is pleasures that my conscience has convinced me are impure even outside of solemn circumstances, including pornography, masturbation, prostitution, and sadomasochism.
The common thread between all those things is the reduction of a person's body - the most sacred object there is (the only sacred object) - to a tool for sensory pleasure; the discarding of anything significant about physical intimacy - or more accurately, the insignificant use of what we still feel is significant. It's not, after all, as if sadomasochists wouldn't object to being abused in general, but that the acceptance of what feels like abuse becomes a source of pleasure - because it feels like abuse. I don't fully understand this dark corner of the human psyche, but I've experienced it myself.
Masochism, by the way, is often misexplained as the enjoyment of pain. That's not what it is. It's the enjoyment of subjugation.