I believe there is no finite answer. A book I might consider too graphic or edgy will be the book that will change someone else's life. It's all about balance. And while I do believe there are some things Christians shouldn't write or read (the excuse of exposing myself to the world in order to be relevant just doesn’t cut it for me), what it all comes down to is each individual listening to their heart and God’s leading. We're all different to reach different people. The eye can't say to the ear, "I don't need you!" The hand can't say to the foot, "I don't need you!"
Sometimes the important stuff is forgotten when we Christians get all into the nitty gritty details of theology and doctrine. Bottom line, let's look at Jesus as our example. He hung out with prostitutes and tax collectors. He told stories that made people uncomfortable. But through all of his teaching, and all of his stories, the thread of grace and redemption was woven. The prodigal didn't stay wallowing in the mud with the pigs. He came home to his father. The Good Samaritan rescued the man beaten by thugs.
What were Jesus' last words to his disciples? "Go into all the world and preach the gospel ..." That's what it's all about for me. And the cool thing is there are countless ways to do it.