The issue to me is that the logic behind why various characters can/cannot be in your party is...lacking.
If Minthara survives Act 1, there is *no reason* that she wouldn't end up back at Moonrise towers, having her mind wiped, ready to be recruited. Slaughtering the Tieflings or not really has nothing to do with her as a character - she only wants them dead because she (wrongly) believes they have the astral prism, and she only wants *that* because she's being mind controlled. Hell, Minthara even calls you out for slaughtering the grove if your reasons for doing so are frivolous.
Similarly, though, while it makes sense that Karlach and Wyll aren't down with slaughtering tieflings, it *does not* make sense for them to leave, knowing that doing so means immediately falling under the absolute's control (and likely ceremorphosis). Honestly, it would make much more sense for those characters to try and kill you than to just up and...wander off to die?
(it also bothers me that the game reacts the same way if the druids slaughter the tieflings as if you do the job yourself, but that's a separate issue).
