That seems like a pretty foolish assumption to make. "Yes evil cult, I totally believe, based off my interactions with Minthara and Dror (who both are arrogant, belittle your character, and give your character commands) that by helping you you'll give me a nice position in the cult and share cult secrets with me."
That certainy dont "seem" like a foolish assumption ...
That IS a foolish assumption! The stupidest assumption i ever heared around here even.
But ...
When you turn it into: "
Yes, evil cult, i shall seem to you all like i totally believe, no matter based on what, everything you say ... i shall bow, i shall listen, i shall be good tin soldier you want ... and once i understand hierarchy in your ranks, i shall crawl as high as possible (and that would be on top), and probably will kill you both in the process ... and then your secrets will be mine."
Well ... if that isnt classic mind set of usual Antagonists (aka Evil characters), i dont know what is.
Regardless of whether such a line needs to be in there, it would make the game better if you could roleplay bargaining with Minthara for your information on the druid grove location. And as @Gray Ghost says, it makes sense that (smart) characters would want to know more about the cult before joining.
I remembered, when i was writing reaction on Gray Ghost ...
(so, if you read the long one, feel free to skip this, since i will just repeat myself in shorten form)
That Minthara actualy is allready promising us power.
True, she didnt call it "unlimited potential of the Dark Side" but "favour of our Goddess" ... but when you get that in context with her character, you find out that is just different words for the same thing.
