AFAIK, all Hunger Demons feed off negative emotions.
I think some sort of variant (that could feed off positive emotions) would be a very cool thing... but that's kind of the mortal schtick. We are uplifted and empowered by our love, by our joy.
I think there was a WOJ that it might be possible for a whamp to feed on positive emotions, but they'd probably start to get 'sparkly'.
Their dietary preferences aren't ingrained, after all - Madrigal proved that by feeding on fear instead of lust. Presumably if they're willing to put enough effort and trial & error into it, other emotions beyond the big three negative ones are possible, with positive ones likely being much more difficult to change their attunement to.
It's probably not an accident that the big three are roughly opposite to the three virtues embodied in the Swords, though.
Lust vs Love.
Despair vs Faith.
Fear vs Hope.
I wonder if Skavis and Malvora tend to lose a lot more of their youth to never activating their powers than Raiths do ... I'd say a majority of people don't have their first sexual experience as true love (as much as they might be confused about that at the time), but blundering into scaring someone to death or tweaking them into despair enough to commit suicide would be rarer.
