Squid: We both know that you were not asking a serious question. It was merely a rhetorical device to express your opposition to gay marriage.
I don't believe we can resolve serious problems by proposing the most extreme scenarios.
As fallible human beings, we cannot always arrive at perfect answers. Nor can we always anticipate EVERY consequence.
But we can propose that we live by general principles that apply to us all equally and, then, if a problem or unintended consequence develops, we can address them.
In another debate on another website on a different topic I used the analogy of telling General Motors, Ford, etc. that they will no longer be allowed to manufacture or sell vehicles because, repeatedly over decades, their vehicles have been recalled for serious defects---and some of them have caused death and severe injury. So despite 100 years of effort and innovation, we haven't perfected our cars, trucks, buses, etc. but no one suggests the answer to the imperfection is to prevent the automotive industry from operating.
What your scenario proposes is that we permanently reject ALL same-sex marriages because some unknown and unknowable number of other Americans whom may be objectionable subsequently might also request marriage status. In short, because heterosexuals were first in line when marriage statutes were developed, they should have a permanent monopoly.
I understand your concerns. I don't have an answer to every nightmare scenario you could suggest. I just don't think we should adopt a principle that states same-sex couples shall be treated differently from heterosexual couples based upon EXTREME HYPOTHETICAL OBJECTIONS. And I trust my countrymen to resolve whatever future problems or unanticipated consequences might develop.