Someone came in here raising a pretty legitimate issue with the presentation and exposition and how the game assumes too much prior knowledge on this core part of the lore...
I absolutely agree with the original post. It's a real issue. Knowledge of Shar should not be taken for granted; it should be introduced in the game.
Lore books and narration are fine for what they are, and I like them.
But figuring out a way to show how evil and dangerous Shar worshipers are would be much better. It would be nice to see a scene showing the Dark Justiciars, if at all possible. We see the remnants of what they left behind in the Blighted Village, and I suppose that's something.
Still. Now that I'm thinking more about this... maybe we shouldn't see them as wholly evil. Bear with me. When we ask Shadowheart about Shar, she gives an answer that puts Shar in a more favorable light. Who's to say that we shouldn't take Shadowheart's view? Why should we jump on the cliched interpretations of Shar that we have as players, as opposed to building a view of Shar from what we find in the game? And in the game, while there are hints of evil, there are also touches of nuance and degrees to consider.
I don't like Tav's potential responses to Shadowheart's revelation, but really, when I think about it, that's probably my biggest problem. Touch up those responses somewhat, and maybe just let the development of Shar play out through the story, either in a sympathetic manner or not.