If it's mutual and there is no manipulation involved, I can't find any immoral aspect in it. But one line of argument can be that the relationship between a brother and sister is destroyed through this choice and consequently the action. It's more likely should be discouraged unless they have fallen in love and are planning to continue a conjugal relationship.. which again will be criticized by the society and culture.

If it is immoral when a child is a child and doesn't know any better or when they are adults. The factor lies that you can not compare a child of incest to an adult doing the same thing on consent. We set double standards as right and wrong. If you are 13 and another is 78 and you both want to break the law does it make it right for one and not the other...

What has incest to do with a belief in God? The questioner is implying that only God (I assume either the Judaist, Christian or Muslim patriarch will do) is the arbiter of a code of morality, but morality has existed since the earliest societies, and often included the prohibition of sexual relationships between close kin.

Why not? Not your business

The question you should have asked this theist is why do the majority of religions believe in the creation story of Adam and Eve. Christianity, Islam, and Judaism! All of these religions claim that humanity is the result of incest! Or maybe that is why the world is full of genetically stupid people.LOL

There is an inhibition in humans and other mammals to have sex with one whom you have known since infancy. Doesn't have to be related.

Christians are hardly in a position to argue the morality of incest, seeing as the bible is rife with it. I believe it is not my remit to condemn 'victimless crimes' but feel in general, the practice of incest is potentially devolutionary and therefore not to be encouraged. It is also difficult to argue a moral standpoint on such issues without addressing the concept of morality itself and that is an inconstant as old as mankind; far older than any Christian ideal.

I would say that the act itself is not really moral or immoral in and of itself, however, the production of offspring from such a union is not to be encouraged. The children would be more likely to have or spread genetic disease and would weaken the overall genetic diversity and strength of the human species.

As a victim of brother/sister incest, ....it is simply hurtful to not know enough about yourself as a small human that you arent able to defend yourself against sexual acts forced upon you by other humans. children are sexual beings but arent ready for physical acts until they go thru puberty. With a no frills sex education and current societal norms in place, children can at least learn to determine what they should do if confronted with incest.

It is damaging to children to have to deal with sexual situations before they are grown. anyone that tells me otherwise needs to be chemically castrated. as you can tell, i feel strongly about this...my brother is not a child predator. if my parents had taught him about his body, hormones, and puberty....i would not be a victim. shame on my parents and its a shame kids are still being denied sensible sex education.

There's a thing called GSA - genetic sexual attraction. Now and then there is a news article about a child given up for adoption that when grown seeks out its birth parent and falls in love. Apparently that attraction is pretty strong when you read the stories and listen to how the participants talk about one another. Granted the circumstances are vastly different than a brother and sister being raised together, but in the eyes of society they are equally taboo.

[en.wikipedia.org]

IF there is some love and caring involved and the couple involved practise safe sex...let them have at it.

With morality being the simple distinction between right and wrong, good or bad, then the very basis for the taboo of incest, that being, that over the history of humanity, it generally caused harmful results. Are there exceptions? Certainly. Again, experience finds the exceptions few and far between. What I find more immoral is the lack of education on sex in general, which I blame mostly on religion.

I don't see anything inherently harmful about the act as long as both are of about the same age. The repugnence is totally a cultural aberration brought about by moralistic religious teachings.

In the long run, it's not something society wants to happen on a regular basis. It's deemed immoral for the purpose of stifling the practice. I voted it as moral, only because the dangers are overblown. I never found my sister in the least bit attractive, so the thought never crossed my mind.

it's just a cultural issue. just like not boning 15yo's is a cultural thing.

Why is it immoral to a theist is the better question. If god only created one couple then he mandated incest for a time. Even without the creation myth science tells us we’re all related. Everyone in the world is no more than 15th cousins to you. It’s all relative, pun intended but sex with close relatives is discouraged by evolution more so than it is by god. I’m not sure any sex act other than Rape can be seen as universally immoral, but it’s certainly unethical and not recommended for all sorts of reasons that one would hope should be obvious with or without a god. When theists ask stupid questions like this or what prevents us from killing/raping make sure to ask them “oh so gods law is the only reason you haven’t fucked your sister/raped/killed yet? Interesting. I’ve raped and killed and fucked as many sisters as I want. And that number is 0”

I have scanned the comments and present this scenario: You have met and married someone in your town or city and you've had a wonderful marriage and raised several beautiful children and you decide to go to one of those DNA site to discover your family history and find out that the person that you've been with is actually a sibling. Now what? They believed that they were morally right. The unspoken truth in society is that many people's first sexual experiences have been with family members. We shouldn't have a problem with it if it's done respectfully. If it leaves a bad taste in your mouth then go wash your mouth with atheist brand mouthwash that's made with plenty of ration. lol. Does morality equal respect?

I can admit that I don't have enough of an education to be able to address this dilema.

Slightly off topic:

Anyone know how the Lanisters make a king sized bed?

They push together two twins!

It’s immoral because familial love lacks a sexual desire, which is probably a genetic program to prevent the deformities and abnormally caused by narrow gene pools. It’s programmed into us as gross, or damaging as mechanism to protect the species, as well as individuals. The disgust reflex is to protect us from threat to health. This person asked you this question because his/her assumption is that Atheists are immoral. Basically, ask her whether it's delicious or healthy to eat shit. Because that is the kind of question they are posing you, and it’s fucking stupid. Of course there is a phenomenon where siblings separated at a young age meet by chance later in life and fall in love and have a sexual attraction. That is understandable and I think very psychologically difficult.

Moral noun "a person's standards of behavior or beliefs concerning what is and is not acceptable for them to do."
So where does this standard come from?
Our society, for lots of reasons, family structure, inbreeding, and so forth.

Why do so many Atheists FAIL to see these are ALL strawmen arguments from theists?
They believe in a God and a religion with its laws, Morals and precepts.
We do not.
Since they cannot PROVE the God and hence the validity of the Laws and precepts, they instead construct endless strawmen. Evolution, Cosmology and all sorts of moral arguments.

"If there is no God why is safe sex between brother and sister immoral to an atheist?"
No answer to this Proves God, it is a strawman.

“Morals” are often simply social mores that have developed because they benefit the tribe. Incest was harmful to the tribe based on issues related to kinship and gene strength, So in that sense incest is culturally taboo, which is the linguistic equivalent of “immoral.” Limiting the question to “safe sex” does nothing to alter the morality because individual instances do not affect sweeping social perspectives. To test this, ask yourself whether you would mind reading about your activity in a certain domain in the newspaper. If you would, then that activity is culturally taboo or “immoral.”

I can't vote because the question isn't based in moraity or lack of it. The answer lies in the history of man as we know it.

It goes against our evolution and instincts. Many animals avoid incest in healthy populations. That is not because of god. Humans just added social taboo.

A surprisingly thought-provoking question. Not least because it provokes a emotional response ("no, no that's disturbingly wrong" ) before allowing oneself a rational response "why is it wrong? Because it is immoral?" When morality is a human invention. Interesting that siblings are mentioned. Incest can also involve father and daughter/mother and son. Different reaction entirely. Even if adult and consensual surely an explotative relationship on behalf of the parent. Yet often younger women seek out a father figure and as often younger men a mother figure as a sexual partner. Latent incestuous desires or no? Egyptian pharoahs regulary married their sisters. Greek myths punished incest between parent and child (usually because it involved patricide to get to the mother). The Doors , The End ... Jim Morrison sings " Father i want to kill you, Mother i want to ... (screams). Culturally taboo to protect the species seems to be the way to go, with regard to siblings at least. (I am discounting child abuse in all of this and only talking of consensual adults). I believe in compassionate understanding rather than retribution and punishment in such cases. As i said, thought-provoking ...

Morality is not a religious concept. It is derived from an evolutionary need for human survival. Incestuous relationships are counterproductive in that they do not provide healthy genetic offspring. Incest is immoral.