correct. even if u kill all the cultists, u still have to sacrifice someone for boethiah to come out.
Really? I just attacked them all and killed them, and now there's one cultist left down there who I take to be Boethia in a mortal's body, because he's got a female voice and complains about being in a mortal shell or something.
Maybe I accidentally killed one of the cultists near the spike and it activated? Dunno why it happened. I actually didn't know you could kill them all to further the quest to begin with, I was attempting to remove the quest from my questlog and route out some Daedra cultists in the process. But then Boethia shows up, I saved and tried to talk to him to see what he says, but I think that quest got bugged for me because the "find the camp" objective wouldn't complete so Boethia wouldn't say any more to me. I just left it, wasn't planning on assisting any evil Daedric Princes on this character anyways.