Extreme danger in legalizing same-sex marriage in society

I do not know of any gene which makes people gay or more likely to be gay. Identical twins are more likely to share sexual orientation than fraternal twins. Fraternal twins are more likely to share sexual orientation than are siblings. Siblings more likely than randomly distributed individuals. Further, the youngest male born seems to have a few extra percent chance of being gay, even if one adjusts for having older males in the family. These are all pretty strong evidence that there are developmental as well as genetic factors. Similar to being left handed or situs inversus, there doesn't seem to be a monogenetic trait which leads to homosexuality. Which is far from saying that homosexuality is not inborn. In fact, studies have shown that homosexuals attraction parts of their brain works like those of females, prior to the conscious thought. Further, I personally never decided to be straight. I just feel sexually attracted to women. I see no reason to conclude that sexual attraction isn't inborn. It's common to find brains wired up to be attracted to men, typically these brains belong to women but there's nothing exacting about human development. Gender identity, gender attraction, and even genital formation have shown a good amount of ability to do pretty much whatever. You only need it to work some of the time to propagate the species. Also, there's some speculation that homosexuals help their nieces and nephews enough to make the trade off worthwhile. In some areas having a rich uncle who never married could allow for genetically related individuals from the family to succeed. So homosexuality may not be evolutionarily helpful for the individual but rather helpful to the larger family and matriarch of the family. The theory seems tenuous, but does make a good amount of sense. However, all of that aside, what does it matter why a person is gay? If somebody were gay for the fun of it, that would still not warrant restricting their right to marriage. Why they are gay doesn't matter one jot. You have the right to enter into a legally binding contract with another person. If you want to marry the person you love, it is not the right of the state to restrict that. Slippery slope arguments are fallacies unless you can really show that there is something to fear. Humans are animals, so humans marry animals all the time. However, for the most part there's a real argument against marrying someone/something that doesn't have the ability to consent. A marriage is a contract between two people of sound mind and body who enter into an arrangement which is recognized by the state and conveys certain rights to the other person. Boys and horses don't really have the ability to enter into contracts because they aren't able to consent legally. As for polygamy, there's a real argument there. I don't see anything wrong with such a contract if everybody involved is fully aware of the situation. The main objection to polygamy is that it often is implemented as polygyny and involves teenage girls being divvied up by church elders. That obviously fails, but additional spouses isn't by default objectionable and would be up to debate. The line is drawn at consenting adults. If rights are offered to somebody they must be offered to everybody. As far as the state is concerned marriage is a contract and the state has no right to restrict who can enter into a contract and who cannot. Yes, I believe those claims are absurd and they are exactly what people were saying about interracial marriage 50 years ago. What's next? I'd assume a complete set of equal rights regardless of sexual orientation, and no special privileges for anybody. Your horse has no ability to agree to a marriage. This is perhaps the dumbest argument against gay marriage. Most of the arguments just come down to religion. If the only arguments against something are religious arguments, then that is simply saying that there are no good arguments for something.