So, if the bakery was known to the run by people with strong Christian principles, what if the baker had refused to make a cake with a message that would be found offensive by many Christians ? Something that would be abusive or offensive if said to the baker's face with the intention of being offensive or insulting.

Well, if that ever happens, let's see, eh? What other answer can there possibly be to all these what-ifs/whatabouteries?