I had never thought of cake as speech before. I read and re-read the first amendment to see if, in fact, cake is mentioned as part of "freedom of speech." It is not. I thumbed through the dictionary and found no mention of cake under "speech" or "talk" or "words."
Why the rush to justify and defend those who demand that their anti-gay prejudice be accommodated? If you think there's a difference, then what you're saying is that homophobic bigotry is somehow nobler or more acceptable than racism and anti-Semitism. And that's appalling.