Specifically: magic, occult, new age, and/or pagan authors.
On Sunday, the UU group mentioned having a pagan library. I was really revolted by this idea. As I told them, and as I'll say here, I'm jaded. Perhaps a better word would be "bitter." As I was just talking to the friend who introduced me to Gaelic Polytheism, I went over two years thinking that all Celtic cultures were the same culture--or close enough to be grouped together. And what is truly irritating about that is that I was reading books about Celtic Paganism. I had books, I was in forums, I was talking about it. Never was it mentioned--or strongly, firmly mentioned--that the Celtic Cultures were diverse and different.
My friend recommended to me to read Special 20th Anniversary Edition of The Spiral Dance by Starhawk. Linked is so far my review of it, and so far why I haven't picked it back up again. The history that Starhawk postulates is grossly wrong and simplified. In fact, anytime I hear "All ancient cultures..." I cringe. Because that is feasibly impossible 99.99% of the time. And then she also pushes the notion that Witchcraft is a religion, which it is not on its own. There are some Witchcraft-based religions, but I know plenty of secular witches.
And Starhawk is one of the least offensive authors I have read. At the very least, she is coming out to acknowledge trans* and include women-identifying people into women-specific rituals. Other authors and pagan figures are not so open minded.
We have Edain McCoy, who I originally thought was a pretty Wiccan-focused book about Celtic deities. Ah... but no, she's much worst than that. Not only is her book not founded in any academic research or findings, but she is arrogant and feels entitled to any culture she so chooses. The website linked there was truly upsetting to read, both by how Éamonn Kearns is that their culture is being commercialized and how uninterested McCoy is with respecting another culture's wishes.
Half Price Books is rather close to my apartment and I often like to visit it. The Mythology Section is, sadly, right next to the Occult/New Age/Wiccan section. There is an entire shelf dedicated to "Shamanism", which I have no doubts is filled with racist ideas of what shamanism is. (Hint: If the person is not talking about Mongols or the Turks, they are probably promoting cultural appropriation.) There are books about the "Old Religion"...However, the only surviving "Old Religions" are Judaism and Hinduism. Unless the book is talking about reconstructionism (which I have no doubt that it is not), then the title is promoting the wrongful idea that Wicca and Wiccan-like religions existed before Gerald Gardner.
So I stay away from self-identified pagan or New Age authors. I'm so sick of the generalizations. Books get published without peer review, or published because they "sound" interesting. I have tried to limit my books to history books, but even those can be troublesome. While I have started reading Peter Berresford Ellis' book The Druids, his theory about how to classify the Druids is Pan-Celtic and uses links to the Hindu culture. An interesting approach, but several GPs I know demise the premise.
I think if someone wanted to learn about paganism, the aren't going to be in much luck with books. I can't think of a single book that encompasses "paganism." Among other problems, there are hundreds of different beliefs. Different theologies. Instead of looking for pagan books, look for what you really want: history, mythology, folklore, herbology, etc. I'm working my way through getting all the suggested books on Tairis' website. The only exception I have is for spell books, since spells and magic can be very subjective. Nonetheless, all books should be looked at critically.
If the UU group does go through with making a "Pagan Library," I may donate books about critical thinking, confirmation bias, and loads of peer-reviewed history books. I'll buy seven copies of Celtic Gods and Heroes so that people can start to stop pushing Greco-Roman ideals onto Celtic Cultures, and hopefully stop pushing it onto others. ...I may also have to borrow the books and critically sticky-note them with fact checks.