I don't the darker content at all. (Within reason, of course.) Recently I have started gravitating toward it. But I am picky about who I write it with. At this time, I keep it to my closest and longest writing partners. We know what lines can be crossed and which shouldn't.
I think it depends on the type of site, honestly. For my animal sites, I absolutely do not allow animal intimacy, but for human sites, it's allowed. Otherwise, boundaries are healthy to have, even with ratings.