All same sex marriage being legal does is expand individual rights. Everything you list as "possible" from the argument you've made is possible now, and has been possible for decades, even centuries, since the US became a country and legally recognized marriages. It's likelihood of happening however is very small. It was more possible to happen back before we had as many different ways to get the marriage ceremony as we do now. In the past, much fewer people were available to perform a marriage which meant fewer choices in who could do a ceremony, but almost the same probability (or possibly higher) that a clergy member would turn a person away when it came to performing the ceremony.