[ikeboy]

>Claimed societal interest in preventing harm to offspring born from inbreeding.

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?

[1] http://www.cdc.gov/hiv/risk/gender/msm/facts/

[foldr]

How would legalizing gay marriage increase the risk of anyone getting HIV? You're not making any sense.

[ikeboy]

The same way that legalizing brother-sister marriage increases risk. Or could you explain more fully why one would increase risk but not the other?

[foldr]

You think that gay men are more likely to have unprotected sex with multiple partners if they get married than if they don't?

[ikeboy]

They might; something being officially sanctioned might increase the frequency.

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".

[foldr]

Are you kidding around at this point? On average, people who are married are going to have sex with a smaller number of distinct partners than people who aren’t married. Gay marriage, if it has a significant effect on gay sexual behavior at all, will clearly reduce the risk of HIV transmission.

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.

[ikeboy]

>On average, people who are married are going to have sex with a smaller number of distinct partners than people who aren’t married. Thus, gay marriage, if it has a significant effect on gay sexual behavior at all, will clearly reduce the risk of HIV transmission.

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?