Uhh, I wouldn't go as far as to allow sex between any age groups whatsoever, e.g. children and adults. I mean, 18 as the age of consult like in the states - that is plain bullshit. Here in Germany 14 is basically the age of consent so long as the older person doesn't take advantage of the lack of sexual autonomy. So you can't just meet up with teens to have sex with them, it has to be in some sort of longer relationship. I think 14 is pretty much the lowest you should go, and 16 the highest. I actually know a dude who's 41 and he met his girlfriend when she was 15. It's a bit unusual but she doesn't seem to be getting taken advantage of or some such thing. I don't see why that would be illegal...

I don't think the reason for having incest banned is religion primarily. The problem is that it fucks up the gene pool and a culture of incest is basically bound to ruin the genetic makeup of a community. Also, parent-child sexuality as a form of incest must be outlawed, because it causes great psychological damage to the child.