just change "consenting adults" to "consenting, unrelated adults".

>funny thing is you'll find some gays who think incest is
>terrible.

i think you'd find virtually all gays think incest is terrible. There's a clear distinction between gay sex, which has no further negative consequences than straight sex, and incest, which causes children with an incredibly high likelihood of being fucked up and dying young

>where do you draw the line?

at two consenting, unrelated adults.