I doubt Tolstoy bothered to ask permission to write a female character when he wrote Anna Karenina. J.K Rowlings obviously couldn't have asked the wizarding world if she had permission to write about their teenage boy hero. Ah yes, you might think, but a man can write a convincing female character and fantasy characters don't count. It isn't the same thing. But it is. If Stephen Hawkings can say that women are the greatest mystery (I'm convinced that he was teasing the reporter), and he's arguably the smartest human on the planet right now, then how could a mere writer ever hope to know what a real woman thinks and feels? And Harry Potter is at his core a teenage boy, which J.K. Rowlings is obviously not. Yet no one challenges their right to create those characters.
So why do people get so worked up about straight women writing slash or white writers writing African-American characters? Part of it is economic. The few bookstores that remain have limited shelf space that they're willing to give over to books about minorities. A queer writer writing queer characters is competing for a tiny available space on that bookstore shelf and the last thing they want is to be muscled out by a book written by a straight person. Worst case scenario: every book on that shelf is written by a writer who is "other." Now readers are left with only inauthentic stories. That brings us to the other part of the problem: identity. Who are the other to tell us who we are?
This might change in the future, but so many people I know first found themselves in a book. They all talk about their sense of relief when they found out that there was someone else out there like them. That person wasn't real, but that didn't matter. If there was one in a book, there had to be more in real life. No longer alone, they took their first step toward finding a community. But as long as the story is positive and relatable, does it matter how authentic it is? I can't answer that.
I consider myself more of a "straight" supporter than a member of the queer community. Yes, I spent most of my teenage years trying to kill myself because I hated (and still loathe) being female. But I'm not sure that qualifies me as trans. I've had sexual experiences with women, and am still drawn to women more than men, but I'm not sure if that makes me bisexual. I know many queer folk and recognize the huge gap between my life experiences and theirs, so I'm more comfortable hovering on the edge of the community than trying to claim to be part of it. But that doesn't stop me from writing queer characters. The way I see it, if I get it terribly wrong, my stories deserve to be mocked, ignored, and forgotten.
My current work is set on an alien world. If she lived on this world, my main character would be a Pacific islander. Her home has been colonized by a country that's a mixture of the city/state of Venice and an Asian superpower. While writing it, I was strongly aware of the two dominant western stereotypes of Asian women: perfect submissives and the dragon lady. The dragon lady stereotype bothered me most because my main character is enigmatic, devious, cruel, and at times inscrutable. Ack! But even if she were a white gal from Scranton, she'd still be all those things. Or would she? My character wasn't born that way, no matter what Lady Gaga might say. My character is shaped very much by the world around her. Scranton isn't under colonial rule. Most of Scranton's population probably doesn’t live in tin shack slums.
I hope that being hyper-aware of the stereotype was enough. I didn't try to refute it by having her do things out of character. What I did was make her a complete person with depth beyond the stereotype. When it comes down to it, that's what we truly want from writers. That's what makes a character authentic. A writer's gender, sexuality, and skin color shouldn't matter when it comes to the heart of human matters. But, of course, the writer has to get the world that character inhabits right too. That's where most of the real mistakes happen.