My thing that raises my hackles is people ragging on me about writing characters "out of character" in fan-fiction. It's my fiction, I'm trying to tell you something, please just LISTEN. I'm a writer (I hope), not a catering service!
That said...I wonder if it pisses you off so much, because maybe it makes you feel misunderstood. You'd rather readers said "Gee, TheAdrians really researched this well, and I know TheAdrians is really smart and wouldn't do this without a good reason, let me read on with an open mind!" Anyway...that's kind of how I feel about such things. "I'm trying to talk to you here!"
Anyway...I find that the best response to such comments is to be very genial and openhearted about it. Sometimes I joke, but I think that tends to give readers the impression I'm not willing to listen to their criticism, so I'm trying to back off of that. So, to this one, I would say "Actually, sickle-cell anemia occurs in xyz populations at abc rate. If you want more info, check out this link!" Usually, if I treat people with kindness, they eventually return it, and I eventually get the kind of recognition that I like.