I have mixed feelings here. When I first read it, I saw just the word "incest" and had a knee-jerk reaction. Then I read that the characters were adults and felt that Amazon was overreacting. Don't get me wrong, if they feel the books would harm their image, they are under no obligation to carry them. However, they were previously carrying the materials. That is like what happened to Yahoo! around 2001 or whenever. They used to sell erotica items until religious groups put pressure on them. That is similar to why the Phil Donahue talk show went off the air in the mid 1990's or so. People didn't like certain topics and themes, so they boycotted all their sponsors.
Even as disgusting as I may think the materials in question could be, I disagree that they should be banned. If we as a society put limits on free speech, where do we draw the line? Obviously, most oppose open racial hatred and promotion of violence. Similar with guides to doing things that are patently illegal like detailed bomb-making guides and particularly dangerous
instructions for making illegal drugs. I don't mean things like how to harvest and cure marijuana. I mean things like making crystal meth or free-base narcotics which cause explosions when done the wrong way. But it gets more slippery and vague from there.
What about suicide guides? What is worse, having a guide of fool-proof instructions to do it right the first time, or having the person trying painful and disabling things over and over until they finally succeed? Who is society to force people who don't want to be a part of it to be in it? Of course, we may argue that children may obtain the information and may follow it over reasons that are trivial to mature adults. "He broke up with me, where's the suicide book?"
Then there are the things like books on how to become obese, how to become anorexic, how to engage in bulimia, and so on. Then there are alternative medicine guides which are often written by non-doctors and make unproven claims. Even what certain doctors write are not much better, like the doctor who prescribed female hormones for nearly any condition, regardless of gender. Then there are the books which oppose abortion or certain sexual orientations or suggest sexual orientations can be changed or converted. Then there are radical books on animal liberation and environmentalism, some even promoting acts of terror. If we ban books related to bomb-making, then why not ban books related to nuclear theory? Every encyclopedia has articles on nuclear weapons, and if someone can manage to get the raw materials somehow, I am sure they would eventually figure out on their own what the books don't tell, if given enough time and enough raw materials.
My point is this: Where do we draw the line? Once we start down the road to censorship, where does it stop? So as bad as some of the above things are or may offend some of us here, I would be hard pressed to want to actually ban any of it. In many parts of the world, child pornography and piracy are being used as covers to restrict other forms of speech like political opposition, mild forms of racism, opposition to gayness, opposition to abortion, fair use of copyrighted works for media purposes, promotion of certain religions, etc. A friend of mine tells me that whenever anyone wants to pass an unpopular law, they nearly always claim it is "for the children." Sure, some of the proposed new laws offer tools that would come in handy to help stop folks who trade child pornography online. However, the use of such tools won't stop there. They may say it is about child porn when it is really about protecting big media. Most of the child porn traffickers use other means to peddle their wares besides PCs. It is a whole lot easier and less risky to swap SD cards, and use a system of arranged drop-offs in prearranged locations. One electronics company is producing wireless sniffers to help find child porn. But they can be used to find ANY type of content, including evidence of file-sharing, evidence of sexual affairs, and personal data.