This is going to be tough staying on topic, the meta topic that is. In strict answer to the title question:
Are questions on topic about when and why the use of certain (potentially) racist expressions might be ok?
I have to say "No," and that they would be considered as list/poll questions.
In the context of asking if the use of some term in an OP-given situation is/was/would be appropriate, then I would say "yes," and hope that the question and answers could be kept in line with the SE "be nice" policy.
It may be appropriate to use the actual term inside the question, though I cannot envision such a case at the moment. Even so, there is no reason the term should be in the title. Titles should never become NSFW, and including known offensive, racist, pejorative terms in the title makes them NSFW.
I refer to "known" terms because there are terms available that are offensive to some people that are not considered offensive, or even rude, in most cases. I have known, in person, people who were offended to be referred to by their visually obvious gender when they considered themselves to be the other, while having done nothing to make that choice obvious to others.
I believe that ELU has a guideline for the use of offensive words, and I think IPS should be even more stringent. ELU sometimes has to discuss the word, or phrase, itself without context, and needs to use the word. IPS is about the behavior, and the exact word probably need never be typed at all. Merely identifying it as a racial, pejorative, sexist, ageist, or otherwise offensive word or phrase should be sufficient to the question and the answers. For the, hopefully, rare occasion when the word needs to be identified, I believe we can still achieve that by using indirection, or redaction: referring to the n-word, or a a***ole, should be good enough. Still offensive in that others know what is meant, yet not actually said.
Lastly, since it's not realistic to expect that every user, especially new users, know, or follow site guidelines. Therefore, it is reasonable for experienced users to do 3rd party edits to correct the posts when needed. If a user insists on doing rollbacks to restore the offensive terms, don't get into an edit war, just raise a mod flag, including the rollback to offensive terms, and maybe raise it in chat if needed.
And, before anyone raises the issue of "Freedom of Speech" I'll remind them that such terminology refers to governmental control in public discourse. Private companies, such as SE and any non-governmental work place, are free to impose any reasonable limits on "speech" that they choose.