What I Say: Your Head Trucker is inclined to agree with Sir Patrick. It is, as he said, a "deliciously difficult" subject: here we are not talking about merely providing a service, but about freedom of expression.
Think about it: would you want to be forced to write or print something that said "No Gay Marriage" or "Vote for Bush" or even "God Hates Fags"?
And how important is a cake, anyway? I wouldn't want to buy a cake or anything else from someone who despised me.