The hiring process is a black box for a reason. The HR department's role is to protect the company first, not the employees, and certainly not prospective employees. If feedback can be interpreted as being discriminatory, or reflective of bad company culture in general, well, word gets around. For much of the time, the reason people don't get the job is that there was someone marginally more qualified/attractive/like…
This. I have done hundreds of interviews, and I used to do a very easy, basic comp sci test. The last question I would ask was, "Tell me about a book, cd or movie that you've read/listened to/watched that was interesting or excited you." The point was to see if the person was engaging with the universe, not to judge their taste or anything else. You'd be surprised how many people get tripped up by this. The worst ans…
Did you seriously grade whether people were "engaging with the universe" (WTF?) based on what their favourite book/CD/movie is and how much they enjoyed it?
Did you seriously dock points from a candidate who obviously didn't care about CDs, movies or books - because he couldn't remember the name of the last record he bought?
Has the thought ever crossed your mind that maybe he engaged with the world in other ways? Perhaps he would hike, or take his kids to soccer, or even play pool and darts on the pub on a Friday. Did you even bother to ask before dismissing this guy as some sort of sub-human degenerate?
Did you actually go home that night and Google Free Bird to see whether or not it was, in fact, an album, and felt a smug sense of superiority when you found out it was actually a longer-than-average single?
More importantly, did you seriously try to convince HR to hire a candidate who was, by your own admission, "not the strongest", because he had "fantastic enthusiasm for literature" and was "quite intelligent" (I'm guessing you based this assertion off of the fact that he read the poetry of Charles Bukowski, and therefore must, like you, be an intellectual).
Mate, I've got some news for you: the reason HR wanted you to stop asking that question most likely had nothing do with the possibility of a religious discrimination case - they either wanted you to stop basing your hiring decisions on batshit insane notions, or stop you making hiring decisions altogether.