You seem to be confusing the issue with your Hobby Lobby example.  Hobby Lobby not selling ghosts and goblins is not the same as a cake artist who sells wedding cakes to straight couples, but not to gay couples.  What if he refused to sell wedding cakes to black couples?  Or mormon couples?  Or catholics?  Hobby Lobby isn't selling ghosts to *anyone* and so they aren't discriminating.  

This guy sells wedding cakes.  He should sell wedding cakes to anyone and everyone who walks into his store.  That's it.