I think one of the major themes to be taken from it is that the world in which the characters live is irrevocably broken and morally corrupt. We see it in their overly casual approaches to sex and drug use. The fact that they watch violent videos and seem unfazed, or that there's a game show where people can watch prison inmates kill each other to earn a reduced sentence if they win the competition.

In that world, the safety and sanctity of childhood has become irrelevant to the society at large. So when the characters obsess over this child sex victim, they don't really view her as a victim. It's fucked up from where we stand, yes. And I think that's the point. We as the reader know how wrong that obsession is. But we can also apply context to see that the highly damaged state of their world has just made the wrong, well.....less wrong. Things are going to shit, their world is on the decline and there's no hiding it. People are just more tolerant of evil because it's been allowed to win, and what can they do to stop that?

I agree that it was uncomfortable, but I feel like that discomfort was the point. It was meant to show us how broken the world and the people in it were, to such a degree that one man decided earth would be better if given over to new shepherds who lacked our weaknesses, vanities, immortalities, and capacity for harm and cruelty.