A few explanations have come out about this debacle besides the "glitch" excuse. There have been attention-seeking man-children attempting to take (unearned) credit for it "for the lulz," as well as explanations and theories about meta-data and filters, experimental ratings systems, some random employee tagging things as "adult," language barriers, and (the crowning glory) a cataloging error.
I don't buy the "I did it for the lulz!" bullshit. That is some punk with a need for attention trying to capitalize on this event because being a privileged wanker is fun. I also don't buy the "glitch" or "error" excuse. The most reasonable explanation is that someone classified anything having to do with "sexuality" as automatically adult, and therefore getting pulled as possibly offensive to somebody, somewhere. My cynical side says its someone who thinks that the word sex is a sin and even thinking about it makes you a bad person, but that's why its my cynical side.
Not as impressive as some sort of conspiracy to silence progressive voices, I know, but still an indicator of a larger social framing issue. The issue resides in categorizing works written about, for and by TLBGQ individuals as automatically about sexuality and conflating sexuality with sex, erotica and "adult" concepts. Having a filter for "sexuality" would lead to the censoring of a suicide prevention guide written by a transperson while leaving a book about treating women like garbage accessible. It would explain why a children's book explaining that some families are not heterosexual gets taken down, but a book about "preventing" homosexuality is left up. This displays a dangerous dissonance in moral categories on a social level, and its a dissonance that leads to ideas like the ones that help pass anti-trans, anti-woman and anti-queer legislation. This displays how unconscious these ideas of misogyny, transphobia and homophobia are in our social consciousness.
So, for all those privileged people in the comments of the articles linked here who are wondering why this matters, laughing about "moral outrage" or mocking those of us who this matters to: this is why this is so important. At best, this event is a perfect microcosm of the ideas that continue to allow people like me, my spouse, and every other gender-variant and queer person in this country to be treated like less than full humans. This is a public exhibition of why we are denied full personhood, again, and again, and again.
If the best reaction you can come up with is "why so srs?" then I recommend a crowbar to remove your head from your rectum before mold starts growing on your nose.
ETA: Or what she said.