Legally, marriage is a privilege regulated by the states, kind of like a drivers license. It is not a constitutional right (doesn't appear there).
Getting rid of legal marriage would, indeed, be both constitutional and fair. It would also be politically infeasible. Can you imagine the political nightmare it would be if we were accurately accused of attacking marriage?
Actually, western civilization and America have honored the definition of marriage as being the union of one man and one woman for centuries. America has known no other definition. In actuality, the founders likely would have tarred and feathered a practising homosexual (not that that makes it right, but some would lie and say they would support gay marriage.)
Who cares?
American legislators saw that marriage as we now honor it (one man one woman) results in benefits for our nation, so long ago they afforded this relationship certain benefits, such as tax breaks in order to promote marriage. Those benefits are order in our society, future doctors, lawyers, soldiers, etc, etc. Can a gay couple give birth to children who would probably someday serve their country? Or become a doctor to help people? No...
No, but lots of straight couples can’t, either. They adopt.
Again, America has never acknowledged any other definition of marriage and we need not change this time honored institution to conform to the whims of a small minority of loud people.
The only thing more annoying than fallacious appeals to tradition is repetitive fallacious appeals to tradition.
Gays can have their rights and dignity without us changing the definition of marriage. They can have their relationships if they wish. They just can't call it marriage. It's similar to me (a man) saying I am now a girl. I am not and will never be. Should I lobby to be called a little girl because girls get scholarships to colleges which boys don't get?
It’s not a reducto ad absurdum unless the thing you reduce it to is actually absurd.
Besides, the abuse you’re imagining is obviously not worth it. You might get a scholarship, but you’d be the target of transsexism. In a hypothetical future world where there is no sexism, transitioning would no longer be painful, but the scholarship that you’re aiming for would no longer serve a purpose, either. So, both in the present world and in a hypothetical perfect world, there’s no reason to prevent people from self-ID-ing.
Genetically, there is no evidence that homosexuality is genetic. Actually, before gays organized and formed a powerful lobby, homosexuality was a diagnosable mental illness as per psychology and psychiatry (look it up). Again, no genetic cause has been established.
So it’s not genetic. So what?
And while homosexuality was once a mental illness, so was hysteria. Hysteria is now just a slang term for “kinda crazy” and homosexuality is now a personality quirk. Times change.
If marriage is not the union of one man and one woman, why not allow polygamy? What about sterile relatives marrying? What about unions between adults and children? People and animals? People would say that is all ridiculous! But what is our standard then for who can get married? What is the definition of marriage if they have their way?
Discussions about weird corner cases like polygamy and cousin marriage are a good argument for why the government shouldn’t be involved in marriage at all.
As for children and animals? They cannot form legally binding agreements, and they cannot understand the social or health impacts of sex, so it’s not okay for them.
In regards to the argument that, "Unsupporters don't believe that gays are human! All men are created equal!", well, there's no argument to the fact that gays ARE people. It's the act of gay marriage and sex that we don't support!
They should be afforded equal protection under the law, regardless of their gender or sex. If Eve is allowed to marry Adam, then Steve should be also. Otherwise, Eve is being given legal protections that Steve isn’t.