Incest makes me so incredibly uncomfortable. I read a Waycest once (Gerard Way + Mikey Way + their sister), and it was one of those things where you can't not read it. But I was so weirded out the whole time.
You have a really good point with the whole exited and horny thing. They usually just go for it instead of trying to go against it like most people probably would.
I think it may be the whole "I can put all my bitch into this character" thing some people do that makes people hate a femal character. After all, most members on mibba are girls and some of the boys are too.
I'm only into slash because I, quite frankly, despise most any female character. I adore my boys. Although, I get tired of the fluffy, repulsive crap that usually revolves around most any slash story. Like, you know, "Ehmehgehd, I'm so gay, and I'm so in love with my boyfriend, and he's so cute, and blegharghableable..."
At least I write ugly, twisted, horrific, insane pieces of slash. Believeable ones, usually. Oh, and the really funny part is that I hate slash incest with every fiber of my being, but I'm writing one. How awful am I? But, no, I'm trying to make this one believeable -- if such a thing is possible -- too. It's coming along pretty nicely, in the sense that two brothers who find that they're attracted to each other should be horrified, rather than excited and horny.
Okay, I'm done with my mellow ranting. Sorry... xDD