You are mixing 2 things that are sort of similar, but not really.  There is no difference between a "gay" wedding cake and a "straight" wedding cake.  They are both made of the same ingredients.  Both require the same amount of time to complete.  They are, by all accounts, the same.  There is, however, a difference between pants and skirts, and dress suits and dresses.  If I needed a suit tailored, I would go to a tailor who does suites.  

A better example would be if I went to a tailor I had gone to dozens of times before to get fitted for my suit I was going to wear to my gay wedding, and the tailor refused saying he could not tailor a suite that was going to be used in a gay wedding - then I would be very upset, as I would feel as though he is now discriminating against me for the fact that im gay.  Its clearly not because he cant tailor the suite - its only because he wont tailor that specific suite because its being used in a gay wedding.