Incest and gay marriage are two completely different things. Two siblings having sex can produce harmful side effects (for example, higher risk of congenital birth defects if a pregnancy was to result from the relationship) . Two men having sex is just that; two men having sex; there are no harmful side effects. I know what you may be thinking; they are more likely to carry STDs. And I'm sorry, but that is simply wrong. Gay men/lesbian women are equally as likely to carry an STD as heterosexuals.