As I am not Webb, I cannot say what was in his head, as a novelist and artist, when he wrote it. But as a writer myself, if I wrote a passage like that, I would be trying to draw from my readers a strong abhorrent reaction to the character performing that particular act. The more descriptive I made it, the stronger the reader's abhorrence would be.I'd wager Webb was trying to paint this character in a very disagreeable way, and used language calculated to do so. How else would you expect an author to depict a homosexual pedophile? With happy bunny-and-kitten language?
The character doesn't seem to be integral to the story line. This character seems to only serve the purpose of being an obscene place marker.
I haven't read the book, but the only thing I can possibly come up with is that Webb was trying to stress the point that people surrounded by war become numb to even the most abhorrent sights among them. If that was what he was trying to point out and that's what he believes, then I think it says a lot about Webb as a person. Decent people do not lose their decency in war even if there are some things that are out of their control. No decent man is going to watch a scene like this and treat it non-chalantly no matter how many horrors of war he has been subjected to.