I would choose to keep LGBTQ+ and African American fiction physically integrated into the larger fiction section rather than separating them into their own sections. As Erin mentioned in her prompt, complete separation prevents patrons from stumbling upon an author or a work that they may not have sought out on their own. In other words, the segregation of sub-genres like LGBTQ+ and African American fiction ensures that these books will only be noticed by patrons who are already determined to seek them out.
LGBTQ+ and African American fiction titles should be visible and accessible for all patrons. However, the separation of sub-genres into physical sections prevents patrons from browsing anonymously. Perhaps especially for younger patrons (or patrons of any age who do not publicly identify as LGBTQ+) seeking resources and literature on LGBTQ+ topics, anonymity is crucial.
One drawback in the decision to keep these sub-genres in the general fiction section is the possibility that these titles will be smothered by the overwhelming and disproportionate number of fiction works created by and for white heterosexual men. With that concern in mind, I would work to promote these smaller sub-genre collections through a variety of passive readers' advisory strategies: printed and online booklists for each sub-genre, rotating displays featuring new titles in LGBTQ+ and African American fiction, and stickers or markers on the bindings of these titles to increase their visibility for the browsing patron.