In my opinion you have to think things through one step further, even if the last post made an excellent point.
Why is incest illegal in most (if not nearly all) parts of the world? And what does it mean to be
illegal?
To address the
why: it is bad from a general genetic standpoint. Bad genes are reinforced and more often then not children born out of incest are unhealthy or have birth-defects etc. That is the entire reason why this is so taboo and illegal.
If you venture into nature, most animals don't care much about those kind of things and it is mostly humans and their care and knowledge about offspring that enforced this rule over millennia, so much that most people think it is an instinctive wrong.
In the case of Da Capo, the state of being siblings is just a label without any real background. Whatever someone outside perceives as right or wrong is utterly besides the point. It matters as much as being left-handed or right-handed. To give an example to those who think about what other people might think: what if they moved to a new city as a couple? Is their relationship wrong there, too?
To be illegal or not is just a society contract. Society has deemed a certain practice as not being good for varying reasons. For not being good for society as a whole, political reasons, public or individual safety etc.
What makes incest special is that it is one of the oldest "laws" there is. People found out that it is not a good idea even before there were written laws. Which makes it a taboo and one of the strongest there is. It is just so plain wrong in the heads of most people, that is seems natural to find it terrible without thinking it through.
Interesting enough, most people are not that picky about laws when it comes to red lights, speeding, making your tax-report, drinking alcohol before you reach the legal age in your area or smoking some stuff that is deemed illegal in your part of the world.
People tend to jump to something not being right or illegal and making it a point when they
feel it is not right. But sometimes you should think about
why.
Ok, that was my 0.02 Euros on the matter
