You need to explain how that make them homophobes.I thought the story was self explanatory, but I guess I'll explain it anyway. The parent was reading excerpts from a book that is found in the school library and was kicked out of the school board meeting for being vulgar. If it's too vulgar to be read in front of adults, why isn't it too vulgar for minors to read it?
Either they are Puritans, which I doubt because they allow the book to be in the library in the first place, or they don't like being exposed for who they really are. The G word comes to mind here.
For the point you actually made, books in a library can't offend people who aren't reading them, reading from them aloud can offend those listening. You shouldn't take a sealed adult magazine from a store shelf and open it and show it to passers by either.