Yeah, and the same themes can go either way. An edge lord trying to push boundaries might write acts that are downright tame for sadomasochistic erotica.

And I think tone is vital here. I've read some stuff that could have been rewritten as horror, but the tone is sensuous.

Lines do get blurred though, pulp erotica is a classic example. My knowledge of it is largely in lesbian pulp, but at the time you couldn't get away with writing a happy love story between two women, especially not an erotic one. You could however write a somewhat vulgar story about a good girl being seduced by a dangerous woman so long as the ending was unhappy for the women.