There's really no moral obligation for objecting incest other than the fact that humans have a natural, offending disposition to it, called the Westermarck effect. We're just following our natural (non-)impulses in that regard.
Hmm I read somewhere that incest doesn't cause as much defects, but a quick google search says otherwise. The rate of defects is to the point where abortion commonly comes into the question, meaning there actually is another moral obligation to not commit incest or not.
In a hunter gatherer tribe you'd except a lot of cousin and half-cousin reproduction, you can get away with that if you're having lots of kids (assuming some will die) and either the tribe's big enough to have sufficient genetic diversity or there's enough new blood coming in through trade and conquest. Siblings can reproduce but it's a desperate short term strategy, parents and their offspring even more so, kind of like chewing off your own extremities to keep yourself from starving even if you survive the damage is permanent.
Morally nothing is inherently right or wrong but just because eating your own disinfected toenails won't kill you that doesn't make it a good idea.
Prove that hurting another person or forcing them to do something they don't want to do is immoral. You cannot. It is self evident.
Proving right or wrong, morals, is an illusion. All you are doing is determining if the belief is consistent and or supported by other moral beliefs but to prove that this belief is valid you prove the others that it is based on are valid.
If morals must be objectively proven then even murder cannot be deemed wrong.
If you use contraception, there is no empirical reasoning against it. But to me, as a Kantian categorical-imperative kind of guy, such things should not be done by a-priori reasoning. Incest is an insult to human dignity, along with other weird-ass sexual activities like looking at child porn etc.
Sometimes in intercourse bleeding occurs for the woman.
Hadoblado is Tasmanian so this means presumably you blame all Tasmanians for this thread.
And because the topic is about incest I must assume that the reason they are so bloody is that Tasmanians would question the right and wrong of incest and generalizing to the whole group (Tasmainians) that incest is common among them and it is bloody.
Where I come from it's just another fun family activity - but then if you've seen the Jeremy Kyle lineup around of any local areas where everyone is everyone's cousin, you'd know this cesspit of a town brings down the average IQ of the planet and sets the human race back a few millennia.
Apart from it being against our nature due to the declining genetic diversity and birth defects that it would bring about, there isn't really an actual moral reason, you are correct. But it is against our nature for that reason, so it is objectionable to us and isn't something I would ever have any desire to do.
Some cultures have done it for some reason - I think it was Ramesses III who I read recently married his own daughter? And according to the author, this was nothing unusual for ancient Egypt.