Yes, but is there a law against someone taking a job due to those factors? Because that's what I see hiring a professional baker is, someone taking a job.
Would you say this applies to restaurants as well? The arguments you made could be seen to apply here as well. If not a restaurant as a whole, does it apply to waitstaff specifically? Waiters/waitresses work for the customers moreso than they do for the restaurant.
I think it's probably a gray area. Depending on how one see's the baker, is she a retailer or is she a contractor? Or is she both?
Making a wedding cake would require a more in-depth relationship with the customer than selling a brownie I would think.
I could definitely pass bad word of mouth around about a black contractor who refused my project because I'm white. But could I attempt legal remedy if I don't have a contract with him?
I think it's a poor business decision on the part of the owner because I'm sure that every customer has violated biblical law somehow (premarital sex, working on Sundays).