The book's apologetic tone about his violence doesn't make it any better - I would even argue that it makes it worse, as it waters down to "extreme violence is okay if you don't feel good about it".
I claim there's a difference between a violent act, and a violent work of literature about that act.
The book spends only a paragraph or two on the actual genocide. No graphic descriptions are portrayed.
If I write, "Hitler and the Nazis killed millions of people in WWII", does that make this post violent? I'd argue that it does not. It's a fairly dry and matter-of-fact description of very violent acts. The post is not violent.
On the other hand, I could write a particularly violent description of a minor fight that left both people alive, but would be far more gruesome and objectionable. There's not a direct relationship between a body count and the violence of a literary work about it.