A flaw with that argument is that no major society has ever recognized marriage between members of the same gender. Marriage has always meant a union of opposite genders.
The nature of humans requires opposite genders for humanity to survive. That some couples may not produce offspring does not invalidate the requirement. Homosexual unions can not - by their very nature - produce offspring.
Comparing homosexual unions to bans on interracial marriage is nonsense.
You err. In addition to the US, the societies of Brazil, Uruguay, France, Belgium, England, Scotland, Wales, Ireland, South Africa, and Canada all have same-sex marriage as a matter of law, however much you or I dislike it.
http://www.forbes.com/sites/niallmccarthy/2015/06/29/the-countries-where-gay-marriage-is-legal-map/