Bestiality and/or incest are _not_ protected classes, and given that we're still writing laws against the activities, not likely to be any time soon. So while I would object to a retailer refusing to sell anything written by/about a woman, a person of color, a person with a disability, etc., I'm not prepared to deploy the same kind of outrage about this kind of erotica. Freedom of speech/freedom of the press does not actively require a retailer to carry all product and thus does not apply.
R. was framing it as an obscenity question. Once I realized that, I was like, no no no, that is not how I am thinking about it. I'm not saying a retailer should or should not carry this stuff; I'm addressing whether or not I think a retailer is being Teh Evil for having a rule along these lines.
In practice, there is no reason to believe that Amazon, for example, has anything against incest (hey, they'll list "Ball in the Family" from 3rd party sellers) or bestiality (they'll sell you "Sleeping Dogs Lie"), per se. I do think they want customers to be happy and keep coming back, which means sometimes the majority preference to not be shocked is going to make things trickier for people trying to find some material for their sexual minority fantasy. I don't think anyone is well served by papering over these differences and somehow suggesting that because some material was removed from some online bookstores, our literary culture/written environment has somehow been damaged.
I'm in the middle of reading _Perv_ by Jesse Bering, and while I applaud a gay man stepping up for better treatment of sexual minorities, I am not overjoyed by how he is going about it. For example, I see "well, animals do it" as a Great Argument to counter idiots who say things like, "well, animals _never_ do _that_", because, you know, counter example, ideally with video. Because _that_ is some funny shit. Just because animals do something doesn't mean _we_ should do that thing, any more than animals not doing something is a perfect argument against us doing that thing (really, gonna give up all your Apple devices that easily? I think not). But labeling the entire area the "Naturalistic Fallacy" without giving more consideration to _when_ it is appropriate and _when_ it is _not_ is crude and unhelpful.
Also, Bering's treatment of our understanding of how we think about the world and make decisions lacks a lot of nuance in important ways.
So I'm sad. I _want_ this to be a good book, but at 10% of the way in, I am Not Happy.