UnderLust was ruined by the fandom. same goes with UnderSwap
At least UnderLust isn't as bad as UnderTail(No this ISN'T A TYPO, IT'S AN ACTUAL AU)
Considering that "Lust" is mostly involving actual Love(Not L.O.V.E.), it's gone to far with the fandom.
It's also supposed to be considered to be an "Adult Topic AU" considering what it is.
In order to beat the game, the "Fight" button is replaced by the "f**k word". So yes, in order to do a genocide/pacifist run, you must F literally everyone in the UnderLust underground(I think that's what your supposed to do, unless that was created by the fandom, then let me destroy literally every word of that-)
Cannon UnderLust itself isn't that bad.