As it happens, the answer is yes. I have recently started working on a novel that focuses on three characters, each of whom has a connection to adoption as well as a connection to the other characters in the book. One of the characters is an adoptee. I'm not very far along in the project yet; the adoptee character is still young. At this stage, the novel is primarily focused on the two other characters. The adoptee will emerge more strongly as a character as the book progresses. I have a pretty good idea of some of the issues she will face, having dealt with them myself, but I don't yet know the specifics of how they will play out in the story.
Do I have a desire to educate readers about adoption? Absolutely! That's what I do on this blog. But the novel is different. If a novel starts with an intention to educate, it is doomed. A novel must tell a story.
No, I am not writing a novel with an adoption theme in order to educate. I am writing about adoption for the same reason Joseph Conrad wrote stories and novels about life at sea—it is what I know. For years I have tried to create fictional characters who have no connection to adoption. It hasn't worked out well, and I think I understand the reason. I can't create what I have never known. Adoption is my milieu, both in fiction and in real life.