> There's no meaningful line you can draw between "I don't sell cake to gay people" and "I don't sell cake to black people". Both are explicitly illegal in most places and morally reprehensible in all.

I agree that both are morally reprehensible.

Can you see the difference between refusing to bake a cake for a gay customer and refusing to bake a cake with the message, 'congratulations to Tim & Steve on their wedding'? The first is about people; the second is about speech. I can live with protecting people; I cannot tolerate compelling speech.