I've been told writing with an agenda is a bad thing. I hear it stifles the story. I don't agree.
I have a four-fold agenda when I sit down to write a GLBT story:
1) Tell the best story I can in a way that will captivate and remain with the reader long after the book closes. This should be EVERY writer's agenda.
2) Promote the normalization of same-sex relationships through repeated exposure to characters with that orientation. The more people see gay characters as ordinary people, the less shocking such relationships become. Julian May surprised me with same-sex spouses in the 80s. But rereads found Gert and Hansi and Felice and Amarie less shocking.
3) Include a transgressively happy ending. There are enough Dead Queer books around. The happy ending challenges the social norm that gays must be miserable or dead by the end of the book.
4) Move money from the reader's pocket to my own in exchange for this story. Again,
every writer's agenda.
Think and know your agenda. It makes for better writing.