Show, don't tell: why they need to be there.
My first reaction was, naturally, "It's not enough because it's not enough." But at the end of the day, that reaction isn't enough, either. He was trying. He wanted to understand. So I figured I should try, too.
I explained how, when I was a kid, the only smart blondes I could find were Marilyn Munster and Susan Storm. How I wound up identifying with the Midwich Cuckoos, rather than the humans who they were threatening, because the Cuckoos looked like me and were isolated like me and no one understood them. How, as I got older and realized that what I wanted wasn't necessarily the kind of marriage my mother had, every gay character became a magical revelation—even the ones I would look at now and think of as stereotyped and cardboard. It was enough for me that they were there.
I don't think I saw bisexuals in fiction until I encountered ElfQuest. I definitely didn't encounter them in sympathetic roles, where they were allowed to be people first, and define their sexuality second. It was honestly a revelation to me.
I explained how important to me these characters were, first because they looked like me, and then because they were like me, and how it mattered for them to have a bigger part in the story than just "oh, honest, blondes and bisexuals exist, we keep them all in Australia because they really like the tax situation there." It wasn't that I didn't want straight while males having leading roles. I just wanted them to share.
I read three books recently where race and sexuality were just sort of there. They didn't change the shape of the story, although they were treated fairly and reasonably (and awesomely) by the author. One, Black Blade Blues, was an urban fantasy with an awesome blacksmith heroine who just happens to be a lesbian, and have a girlfriend. And while she had some personal issues to work through (which made her a compelling, relatable character), her story was still recognizably an urban fantasy story, with all the tropes and twists of the genre. The second, Storyteller, was science fiction/fantasy in the Pern style, where you have extremely advanced technology and fascinating aliens, but you're spending most of your time on a low-tech planet that might as well be a fantasy world. One of the central characters is gay; so are several secondary characters. None of them are treated in any way as either superior or inferior to the rest of the cast.
The last, The Hum and the Shiver, dealt more with race than sexuality, although it was notable for having a strong female lead who really enjoyed sex, had really enjoyed sex in the past, and was not in any way ashamed of herself for being a sexual being. It's not a sexy book; she actually has no sex during the book, for reasons the plot makes very clear. But she's not punished for who she is. One of the secondary characters is married to a Southern-raised Asian woman. Why? Because that was who she was. It's not a thing. It's never a thing. It's awesome.
He was still a little confused, so I tried another tack: in my Faerie, in Toby's Faerie, as far as I'm concerned, almost everyone immortal is also bisexual. People who are purely straight or purely gay are almost entirely changelings, and young changelings, at that. Out of the entire current cast, the only one I can point to and say "Yup, totally straight" is Toby, who was raised in the mortal 1950s, and never really considered girls as an option. Everyone else is bi. Yes, him. Yes, him, too. Yes, her. I'm not sure it counts in Lily's case, since she's a body of water that enjoys looking like a person, but she doesn't care about the gender of her meat-based lovers. So yes, even her.
Most fae marriages, on the other hand, are male/female, because the main motivator for fae marriage is having kids, and surrogacy isn't really an option when it takes three hundred years of steady marital relations to reliably get someone pregnant. So if you look at the first several books, everyone looks straight. I was too close to the material to realize that. I knew about Amandine's relationship with Lily, the Luidaeg's long-term Selkie lover, and lots of others. No one else did. What was on the page was heteronormative male/female love, over and over again, in all its good and bad forms.
As soon as I recognized that, I started making more of an effort to actually show the non-hetero relationships in the books. Not because I owed anyone anything. Not because I was pressured. Because saying they were there wasn't enough. It's never enough. We need to see those people, in part because for every kid like me, combing the margins for hidden people I could relate to, there are ten kids who just calmly accepted than yes, they were always going to be the protagonist. Mix it up. Make it different. Make us all learn to identify with other people, and take out the shadows. I learned to identify with straight white males because I had to, and I clung to my narrow band of options. How about we widen the spectrum until everybody gets the chance to learn to identify with everybody? Because that would be awesome.
I explained all this to my friend. I think he understood. And even if he didn't, he's thinking about it now, and he's smart; he'll get there.
I'll be waiting for him.
(*I won't name him, because that's not the point, and he's a damn good guy. He just hadn't thought some things through. Everyone has had their instances of not thinking things through, and it's easier when you're a middle-class white male with no particular religious affiliation. Everyone is you unless stated otherwise, in fiction. So please don't ask who my friend was, and I won't be forced to look at you sadly.)