I am at a loss for words. I'm not quite sure after reading the article how I would have approached it. As librarians we can only hope that the father would be supervising his sons. I doubt the book was on display or anything where they could have easily found it.
There are many sights, sounds, smells, etc to be disturbed about. Some things have become facts of life. Everyone can be offended by something at the library--and every other public space. Hopefully this case doesn't set a precedence for an even lower standard of the-world-revolves-around-me syndrome.
The librarian should have asked the man where his children found the book. When he was sure to reply "I don't know", or "In the Adult section", the librarian should reply that children should be monitored by their parent or guardian while in the library, and that the Adult section contains many books inappropriate for children, for many reasons. I can't believe the library buckled and pulled the book. That makes that man's court case stronger!