Society doesn't make incest something we frown upon. Incest itself makes society frown upon it due to the risk factor in offspring. I don't think there is any species that reproduce through incest. It's not a social thing, it's a instinctual thing. It's built into our genes that incest is bad.

I think incestous feelings are okay because if you like someone, you like someone. But for your children's sake don't do it.