I also know married straight couples who've adopted children rather than having their own - are those fake families? Would a gay couple who adopted a child be creating a fake family?
The only thing consistently binding marriages across cultures in the US and my own country, IME, is that two people have agreed to love and care for each other "until death do us part".
I'm not ever going to have kids with my girlfriend, am I to be restrained from marrying her?
My mother was well past the age of childbearing when she married her current husband.
Your argument doesn't hold water.
My getting married - according to my definition of married - doesn't affect you in any way, shape, or form, so why would the Government prevent me from doing so?
I never did get to the bottom of how that was supposed to work.