Still not sure what the issue is.
A. They should read the article as it specifies the character isn't a Slayer, just a normal guy who slays vampires and would like to be a Slayer.
B. A gay character. Willow, Tara, Kennedy anyone?
C. A male gay character. If one finds a female gay character acceptable but not a male one, then I'd say that's maybe more stupid and offensive than just flat out not wanting any gay character.
That is all.
They aren't annoyed that there is a gay male character, they're annoyed that a male character is being introduced with the title of Slayer, which other badass normals haven't been so far, and arguing whether it's only being done because he's gay, and whether this means equating gay men with women etc.
Personally, I think it's people making too much fuss and judging a story they haven't even read yet, but I'm just saying what they're debating.