Well, they asked for a pretty clearly worded political message to be put on the cake - effectively asking the bakers to produce something they do not agree with. For me that is forcing your beliefs on others. Fine for them to be in support of gay marriage, fine for others not to be.
I agree re: not being told you are outdated, but surely you also agree that views should be changeable and not set in stone, that we should be open to new ideas and thoughts in general?
Well, do you still think the earth is flat? If you were born many years ago, you would. It was accepted as fact.
I don't think it's the same as fashion. Views should change as greater evidence for new facts are understood/revealed.