Sarah Bonner has been an Illinois middle school teacher for 20 years, and she has always tried to offer her students a diverse collection of books. One of those books was Juno Dawson’s “This Book is Gay.” It’s a bestselling nonfiction book that’s billed by its publisher as an entertaining and informative “instruction manual” for anyone coming out as lesbian, gay, bisexual or trans. “By Wednesday, I received notice that parents had gotten a hold of pictures from that book that their child had taken in class,” Bonner says. “By Friday, I was told that parents had filed a police...