If that's all, it seems that logically, brother-brother marriage should be OK.
I suspect the real reason for a lot of these laws are is "because it's icky". The justifications seem more like rationalisations.
On a serious note though, you allude to one of my favourite aspects of law. Throughout history, views on brother-sister marriage have changed. At points/places, it has been perfectly fine for brothers and sisters (especially in elite families) to get married.
I am far from an expert in this field so can't speak to why our norms changed. If you want to take this further, you should start with the Westermarck effect and look into the kibbutz study. Or, maybe consider how marriages between families evolved as a way of formalizing business or other strategic relationships. Either way, taboos are cool!!
For example, in ancient Greece, homosexuality was fine. Hell, even Zeus advocated it as a way to prevent pregnancy. Yet, by the early 1900s, it was considered mental illness through much of the world. Taboos are always in flux and I can't figure out why. Logically, you'd think that science and information sharing would make us all more liberal and taboo-proof, but I'm not sure that is happening.
I think you're right - but i also think you're underestimating the lack of science minded individuals in the ones who are less liberal (such as in the US).
Education is becoming a big problem, in general.
There was a case in which this happened, the "Blue Fugates" [0], who had a particular recessive disease[1].
[0] https://en.wikipedia.org/wiki/Blue_Fugates [1] https://en.wikipedia.org/wiki/Methemoglobinemia
This argument made sense before genetic screening was available, but falls apart with genetic screening, since you could screen the siblings to see if they are both carriers.
There are enough cases to realise this is something of a problem, although protections can probably be built into the system.
Children (minors and the "age of majority") and age of consent is defined by law. While we have come mostly to an agreement on the age of consent for many things, nothing prevents us from changing our definitions or age of consent for varying activities.
The legal framework of consenting age protects the abuse of a minor's inability to "think like a grown up", though it's arguable if the age of consent is too low (because biology dictates an older brain has a matured executive function capacity) or too high (because some kids, as many can attest, are wise beyond their years).
Should be "Current western and developed/modern civilization's legal framework of consenting age"...
If that's a valid argument, why isn't the same argument [1] against gays valid? Conversely, if greater risk isn't enough of a constitutional reason to allow bans on gay marriage, why is it enough to make incest bans constitutional?
Can you at least see a reasonable comparison between the two? If you don't think changing marriage laws affects behavior, shouldn't that apply to incest as well?
It seems to me that "legalizing gay marriage won't increase gay sex overall" and "legalizing sibling marriage won't increase sibling sex overall" are likely to be inconsistent with each other, and that the first is implied by your wording; if gay sex increases, it should also increase "unprotected sex with multiple partners".
With regard to sibling marriage, the issue isn't sex per se but children. Although I am not myself deeply opposed to sibling marriage, there are many couples who strongly prefer not to have children outside of marriage, so it is quite reasonable to assume that banning sibling marriage will reduce the number of children of siblings. In contrast, it would simply be laughable to suggest that any significant fraction of gay people who have unprotected sex reserve unprotected sex for marriage. If that were so, HIV would not be a problem in the gay community!
So, no, there is obviously no reasonable comparison between your two cases, as a few moments of thought would make clear.
You're neglecting the possibility of increased gay sex due to wider acceptance, which would affect even unmarried gays.
Can you make the argument for higher risk from legalizing incest in your own words, so we can see why it wouldn't apply here?
Gay marriage would most likely have no significant effect on male-to-male HIV transmission rates. In contrast, it is quite obvious that legalizing sibling marriages could encourage siblings to have children, thus increasing the risk of babies born with genetic defects. That being said, it is not clear to me that this constitutes sufficient grounds for making sibling marriage illegal, and I am not strongly opposed to legalizing it.
If you seriously think that there are lots of gay men out there just waiting for gay marriage to be legalized so that they can have lots of unprotected sex, then you really need to increase the diversity of your social circle.
Is there any difference between the two that's relevant legally? And do you have any more robust defense for the distinction? Your argument above made some sense when distinguishing overall gay sex increasing from risk increasing, but you seem to have abandoned that in your last sentence.
>If you seriously think that there are lots of gay men out there just waiting for gay marriage to be legalized so that they can have lots of unprotected sex, then you really need to increase the diversity of your social circle.
I could say the same about sibling marriage for you. "If you seriously think that there are lots of siblings out there just waiting for sibling marriage to be legalized so that they can have lots of unprotected sex, then you really need to increase the diversity of your social circle."
I wasn't expressing any opinions on what any particular law would lead to, just that the reasoning being used was inconsistent.
>You can't just imagine any old wacky scenario and use it as the basis of your argument -- it has to be plausible.
But this exact scenario is the basis of the argument above against sibling sex.
Yes, the difference between how gay marriage would affect the risk of HIV transmission vs. how sibling marriage would affect the incidence of genetic defects in babies.
>Your argument above made some sense when distinguishing overall gay sex increasing from risk increasing, but you seem to have abandoned that in your last sentence
I'm not sure what you mean. Gay marriage will neither increase the total amount of gay sex nor increase the risk of HIV transmission. There is simply no connection between HIV and gay marriage, so it would make no sense to try to use HIV to justify a ban on gay marriage.
>I could say the same about sibling marriage for you
You could, except that it wouldn't be true. Having children outside of marriage is still a big deal for a significant number of people. Unprotected casual sex is, virtually by definition, not something that appeals primarily to people who want to get married. Again, the facts are important. You can't just make up crazy hypothetical scenarios and use them as the basis of your argument.
When disagreeing, please reply to the argument instead of calling names. E.g. "That is idiotic; 1 + 1 is 2, not 3" can be shortened to "1 + 1 is 2, not 3."
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They didn't have to include the postscript. It came off poorly. I'm not posting this to social media trying to get OP fired, but I will call out when people include contentless swipes at other peoples' legitimate posts.
Does this mean that marriages between same-sex siblings will be permitted?
It's simply the fact that we find the idea of siblings having sex to be icky. Which is the same reason for the prohibition against same-sex marriage.
http://www.genetics.edu.au/Publications-and-Resources/Geneti...
Etc.
Bullshit [1].
Children are not considered capable of consent.
> Why not allow brothers and sisters to marry?
Claimed societal interest in preventing harm to offspring born from inbreeding.
> I'm not trying to make a slippery slope argument. I'm really asking.
OK, well now you have a couple answers.