The Librarian for the Black Lagoon is one of many books in a series that teach kids not to be afraid of something they have not experienced simply because they've heard scary rumours from other kids. Other books by Mike Thaler and Jared Lee (illustrator) in this from black lagoon series include, teacher, principal, gym teacher and school nurse. Obviously most kids will have been to a library by the time they are old enough to read picture books and even before that not too many are afraid of libraries but it does highlight to kids how silly it is to be scared of something they don't know and to believe stupid rumours which they can use to think about other stuff they may be scared of. Also useful in comparing to eating healthy foods they've never tried but think are gross and things like this.
Basic plot is the main character finds out his class has an excursion to visit the library. Himself and the other kids have been told probably by older kids (the source is never revealed) that really strict rules apply at the library, it is a terrible boring place and if they disobey the librarian or library assistant they will be laminated, electrocuted and other terrible things. Of course when they go to the library they are in for a big surprise.
The illustrations by Jared Lee are very basic but very well done and actually make the book funnier than the text alone.