Works of art -- books, movies, music -- help shape our world. We learn from them. We let them in. We use them in our daily lives -- they give us advice, we quote them to our friends, we save a little piece of memory for each of them. They become a part of who we are.
Sometimes, the creators of these books are what we consider criminals. They may be pedophiles, mass murderers, serial killers, rapists and torturers -- those who hurt other people, those with little regard to human life.
But we don't know, and we let them in. Or let our kids explore their dark worlds and follow their twisted minds. Who knows what effect their words will have on our kids a year or two from now? How long will it take to discover that the book you just read is a product of a sociopat and a maniac?
Mark them.