The Romans knew that control over marriage was their power. Before you cry out loud for fact check upon their acts, consider that family intervention was their key into human experiments. You were taught about how they made people compete against each other, but did anybody ever tell you how they gained loyalty? It was meant to increase population. Beyond the distortion level, what you know today is there are doctors that continued their means of such practice; where they have overridden all family values, desires, religious expectations, and gutted the very essence of natural birth.
However you argue your next point about that, the father is no longer the man he had been before that moment of intervention. The mother no longer saw her man had the control she needed. Statistics showed that such mothers gave in to authoritarianism, as they coped with each shock of their new reality.
The reality, today, is about "gay marriage" and how we got here to this question about it. Can you define gay? If you mean homosexual then, why not say that instead of ruin the truth of the word "gay" with such notions that have nothing to do with it? I believe two homo-sapiens of opposite sex must be married before either one can consider themselves gay. Now, I heard people claim that they are born gay, so how is that possible? Maybe as I wrote above, something unnatural.
The natural semantic "homo-" is being human. I heard arguments that "homo-" meant oneness, but that doesn't make sense if you say "1 homo-sexual." I think it is obvious that the fetus is its own gender, and its next gender is hetero-sexual in development. That "hetero-" development continues into adulthood. At some later point, people realized their development changed into "homo-sexual" gender. All earlier hormones wore off that made them quite different in their thinking between the sexes, and they are now older and being human. Being gay is intangible to all those events, and being gay doesn't include any tangible paramour with anybody.
I have noted elsewhere that the outer shell of the historic atomic bomb is said "gay." Detonation of the bomb required great amounts of reflection and severe rainbows of frequencies that literally obliterated the inner metal through implosion until it finally exploded. That is the most stable definition of "gay."