Originally Posted by Plancer
Cliffs cliffs: Feel free to only respond and read the sentences that are bolded. To make this easier for you, here they are again: "yes, you're right, but that isn't the reason incest should be illegal." and "How does his criticism of the incest taboo, if acted upon, have any effect? "
Cliffs:
The OP is correct regarding that anti-incest laws, when enforced upon consenting rational adults, are anachronistic and an unlawful. However, he doesn't show any examples of how this matters, as it appears he would agree that most illegal incestuous relationships should be illegal because they are almost always rape.
My post provides evidence that the OP is right about the law's effect on the genetic robustness of the population, and while the OP is right about this being obviated by birth control, there is no evidence that this goal has existed in the post-Hitler West. Furthermore, there are relevant examples in reproductive law. In other words: "yes, you're right, but that isn't the reason incest is illegal."
War and Peace Length:
The argument's conclusion in the video is correct with regard to fringe cases.
I must timidly admit the OP argument is technically correct. However, he doesn't show how it's relevant. How does his criticism of the incest taboo, if acted upon, have any effect? (In other words, what relations ARE prohibited that should have been prohibited).
He provides a reasonable and powerful proof that this statement is correct: "Laws prohibiting incest are based on preventing a potential side effect which is now easy to prevent."
This argument ignores the standard conservative utilitarian response - frequently an irrational, incorrect, or obviated basis for a law has little to do with the law's outcome. An obvious example would be Brown v. Board of Education, where a great deal of the anti-segregationists' argument was based on faulty psychology regarding black self image (for instance, evidence such as black children using negative adjectives to describe black dolls and positive adjectives to describe white dolls was incorrectly accepted as evidence of segregation's harm).
There currently are NO laws in the US which prohibit any sort of human breeding or genetic selection. If you want, you can get a designer baby with super-potent Huntington's and there are no laws against it. This sort of human freedom to generate babies is, as far as I know, universal in the West. The closest to a restriction that I know of is it is illegal to select for an embryo with a genetic disorder when doing in vitro in Britain (a far cry from dangerous mating). Obviously, you can get around it in any area where abortion is legal (yes, I realize how unfeasible this is).
These lack of restrictions (or restrictions) to embryo-selection are not irrelevant, and is illustrated with the deaf community. Most deaf parents would prefer having deaf children, and many in the US select for this. It has recently become illegal in Britain to select for deaf embryos, and there is a movement against it, albeit small. The issue of deafness and civil rights is very complicated, and although restricting the creation of deaf children might appear obvious, it most certainly is not. Furthermore, the compelling argument to preserve the deaf's right to reproduce applies to a host of other disorders (most notably dwarfism).
Although incest is clearly genetically inferior to random mating, it's very easy to generate examples of non-incestuous mating which is inferior to incestuous mating - it is trivially easy to show that the average child which would be generated by a randomly selected incestuous pair is better than the worst 1% of pairings (simply observe the incidence of autosomal recessive genetic disorders). Although I'm not comfortable setting a number, it is obviously much higher than ~2.66% (1 incident / 1.5 children per couple *4). If there is a rights-based rationale for protecting potential children of incest, it must apply to these people as well. The percentage of dangerous pairings is too high to give reproductive carte blanche to the unrelated while restricting the related. Put another way: if you want to use the argument of genetic risk, get ready to arrest 4.5 million married Americans.
Are there utilitarian arguments for restricting incest? The answer is an obvious "no." The cost of detecting dangerous pairings has fallen so low that any sort of utilitarian argument fails on a cost-benefit analysis. The only form of the argument which would make sense is "we would like to restrict many reproductive pairings, but hey, it's really hard to get people to agree to that because it looks like Hitler's Germany. So we'll settle with keeping incest illegal." Normally I wouldn't have to concede this point due to the social stigma, but hey, this is 2+2 and there are some very logical posters with some very big balls.
So yes, the OP is right that the anti-incest lobby (a fearsome force indeed) frequently employs a completely invalid argument, and yes, the genesis of this law may have some utilitarian component. However, this positive effect is not valued by our society. Furthermore, there are other positive effects. Lastly, he does not show any cases where incest laws have a negative effect.