The most "remorse" I remember him feeling was for killing Cassius' brother (whatever his name is), but then it felt more like he was just afraid of Cassius than feeling sorry. I wouldn't really have an issue with him murdering people left and right if it was played as the "you become the monsters you battle" trope, I don't know, it may be just that in the other books, I haven't read them. But I doubt it since