I think reading that stuff as a kid did desensitize me to sexual content in fiction. But didn't affect me in real life circumstances. Same probably goes for the kid, heaps of books, shows and games feature death, doesn't mean he's suddenly going to turn violent, just means he'll get used to seeing that stuff in fiction.

When I was 14 my mum gave me a fantasy novel called Tender Morsels. In the first few chapters of the book the main character (who is around 15 at the time) is raped twice, once by her father and the second by a group of village teenagers. And she gets pregnant both times. My mum had no idea what kind of book she'd given me. Oh, and I read the whole thing anyway lol.