I couldn't be bothered to read through 18 pages of this debate honestly. I'm not too interested in participating on a one side or the other fashion. I did however want to add my perspective.
Why is my perspective relevant? I used to be the "prurience czar" on the image side of things at Amazon. What that means is that I was the one who policed what was and wasn't "acceptable" to display on their site. I wasn't involved in choosing what titles were or weren't sold mind you. Just in what imagery was acceptable. So while it's not the same as whoever opted to remove this title from their catalog, it's related. And it did lead to working with the marketing people that made those sell or don't sell decisions. So I have some inside poop.
Here's the thing ... they do have some definite lines drawn for what 100% can't be on the site. Then there's the grey area. Flagged stuff that has to get a thumbs up or down from someone. And yes, they work in a reactive fashion. The reason being that the percentage of things that would get flagged is fairly small. And the process to get things online would be seriously hobbled if everything had to go through the filter (part of my job was developing our processes for getting stuff online). So that means "bad" stuff often goes up and then gets pulled, rather than not going up at all. Ideal? No. But generally much more efficient for the 99.5% of product that isn't an issue.
For things in that grey area ... it's ... well ... grey. I was a lowly Photoshop jocky but debated VPs over images of naked man butts. And that's where the inconsistencies come in. If the person in charge of the catalog content get's word from someone higher up to pull something, they'll often pull it, it's what they're told to do. And often those higher up's aren't necessarily as altruistic as the catalog programmers, who are often in those jobs because they love books, etc. So if there's isn't the right person in place to defend a title, it'll get pulled.
There's a book called "The Toy". Innocuous title. Image of a woman in a cage, not a nun, but not naked. Ergo, fairly innocuous image. Neither alone an issue. However, the combination of the word "toy" with the imagery of a subjugated woman caused friction. Kids searching for playthings got S&M erotica.
Books like How to Rape a Straight Guy end up in similar conference calls. And if there's enough pressure, the person who actually handles the catalog would most likely choose to keep their career path clear rather than duke it out. You choose your battles.