The US Constitution is silent about gay marriage. As a matter of fact it is silent on a vast majority of issues encountered by humans. The idea behind the Constitution was not to “protect” we citizens, but rather to grant certain very limited powers to the new Federal government in order that it might conduct our business. The Bill of Rights were enumerated to assure a more limited form of government…a deep concern of many at the time.
The 10th amendment specifically says, “The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.” Under these circumstances, gay issues are clearly within the domain of the people. Should the citizens of a particular state wish they may regulate these and other items of human behavior they can do so at the state (or local) level. They are also free to simply ignore the issue.
In the end it is, “We the people,” who determine how actively our various governments intrude upon our lives through our vote. The majority dictate the course of our legislative involvement upon the minority.