For me, a 1 is racism, sexism (a focus on the way women characters look while the men are just a name, all the women in the novel are stupid/shallow/careless, descriptions of breasts), or terrible grammatical or factual errors (one author confused the Civil War with the American Revolution... just HOW????). Most of my 1s have been self-published works from Kindle Unlimited.

Imagine a gay kid who doesn't have support at home going to the library to stand in a segregated aisle like that. Or, books are not segregated and the kid can check out the one that interests him or her without the chance family members will notice what type of book it is. This is important because not everyone can safely come out of the closet.