To me that means the only logical course of action is to start off by considering her as evil, regardless of what I find out later. At the beginning, the only valid opinion a character can have is that she's evil. As other evidence comes in, it's perfectly reasonable to question whether she's actually evil, brainwashed, or something else based on the evidence. But if you accept the later evidence that she might not truly be evil, you have to accept the initial evidence that she should at the very least be treated as evil when you first meet her.
This^.
I think Kanisatha's problem, and the problem of many hough not all other people who don't like the companions and think they're too evil isn't an in character one, its entirely based on the fact he as a player has that information and does not want to spend his time in a game that's supposed to be fun consorting with someone he considers morally reprehensible.
As for the difference between worshippers of Shar and Umberlee, to be a Sharran you have to have betrayed and murdered somebody, ideally a loved one. I don't think Umberlee has that same requirement. Thoughni too would like to hear his rationale. And regarding knowing Shadowheart is a Sharran, any have pointed out that onyx disks on her armor are pretty big give aways. And I'm inclined to agree based on the fact we know she's a cleric and if the only identifying aspect of her armor is stone sacred to a deity, that's a pretty strong hint in-charscter.
And this^.
These are my arguments exactly.
