I am not going to respond to everyone. What I will say is that this clerk is entitled to believe what she wants and so are those that believe she is wrong. Each person is a moral being created with intrinsic value and worth. People are free to believe that marriage is between a man and a woman, or they are free to redefine marriage to mean whatever they want it to mean (like what happened this year). Both views take a moral stand and make an absolute claim for their beliefs: each side believes that their belief is right. It would be ludicrous to believe, as moral beings, that everyone is going to agree with everyone else, or that everyone should be forced to believe what the other believes.
My person complaint is that I see (as do others) history about to repeat itself. I think Herbert Butterfield's (Regius Professor of History and Vice-Chancellor of the University of Cambridge) analysis on human nature in the aftermath of World War 2 explains the clash of worldviews that this thread and many in the United States espouse and ultimately where it will lead:
Regardless if what a person believes, history bares the scares of what happens when a society declares one side to be morally incorrect and at some point does everything in its power to eliminate those that hold to a contrary point of view. There is just no way this is going to be avoided.