Are we actually sure that the Cult is a part of our tadpole alterations. I'm not sure if its two parties or three with the Mindflayers implanting, the Cult hijacking and then a third party messing with ours.
I don't think we do know for certain, but they do seem like the best lead we have at the moment, given that all their True Souls have tadpoles. There is clearly some connection, as all these tadpoled individuals are ending up in the group, and though we don't know what that connection is, it does seem reasonable to me to hope that if you follow the thread it will take you somewhere useful. I think if I didn't particularly mind killing a bunch of people, then trying to get in with the cult would be the option I'd go for in order to save my life, over the extremely dubious help Halsin could offer given Nettie and then he confirm that he's not sure what's going on with them. So I'd probably say that it's a path extremely selfish evil characters could easily choose as well as those who might hope to get any additional benefit from it.
Of course, it might be disappointing if their evil plans are scuppered before the end of chapter 1 because the Absolute and her minions are onto you, though that doesn't mean it's not what a character would have tried to do. And it could even be done well: okay, plan A didn't work, but with any luck you've made some new allies in the form of Minthara and her drider pal, or if not you've burned a whole lot of bridges and need to find another option ... on to the Githyanki Creche, perhaps! As long as the game keeps giving new options and reflecting my choices I don't actually mind if things don't always come off as I'd wish. Though, as you mentioned before, I'm not sure I'd be happy if the game let me make choices that made it impossible to finish the quest down the line.
