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

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the author wasted it on the other "red" guy.

In the first book to me it came across as a simple power fantasy.