It's a little hidden. Shadowheart actually remarks on some of your evil works commenting "A small child could have burned ___" to the ground Also has a unique and very telling option when opening the book of thay.
Zae...well she disapproves, but still makes comments on the opportunity to kill.
Astarion replies with levity when you talk about certai evil deeds.
Gales....as long as you give him magic items to eat, meh.
All of it is extremely easy to miss, so if you miss it dont worry too much about it.
