1. Moving materials to a separate location can discourage use, especially for young people who may be questioning their sexuality. By moving this material to a separate section, the young person may be too embarrassed to look for books in the "special section." In this case, you have effectively made the books off limits and denied information to the people who need it the most. By creating a separate section, you have effectively said "these people in these books are not the norm" and we don't want to send that message to our communities.
2. By putting these things in with the regular collection, patrons may be more likely to stumble upon a book and choose it without knowing exactly what it includes. It removes the bias of choosing a book about someone who is different than you are. And hopefully, patrons may read about these people and learn a little bit about their history and their lifestyle, and perhaps remove some of the stigma these people face.
3. If we create sections about GLBTQ and African American fiction, where to we go next? Where do we draw the line? Should we remove all other nationalities to their own section? Do we create a heterosexual section? Who decides what gets placed in each section? If there's one marginal gay character, is it GLBTQ? This opens up more confusion than what is necessary.
So, say you have a population asking for it, who doesn't want to marginalize it, but instead celebrate it and promote the materials. You can still do this through readers' advisory, book lists, blog posts, and book displays. Make it easier for your patrons to find this materials while still integrating it into the regular collection.