Incest

I don't find it as bad as most people find it to be but makes me feel sick if i were to ever think of my own family like that :S

I think if you're trying to rub one out to a doujin, hentai, or whatever is fine the whole forbidden love thing I get it. However practicing it in real life is just fucked up.

Lol, well they are still family, so yeah

In real life, you get genetic disasters who will live a badly reduced quality of life because of some fucked up nastiness between relatives of gratuitous proximity. In the manga/anime world, I still haven't touched this genre or anything that includes it. I have six younger siblings. It's disgusting to me.

Not only would that be illegal, but also immoral. And I'm not a Bible thumper, but whoever wrote the ancient editions knew to denounce that, at least.