In liberal U.S. courts, the bakers would have lost.
The judge would have stated that the message was “by the gays” and that the bakers were not creating the message, just planting someone else’s message on the cake.
On the other hand, why couldn’t the gay couple have just taken the cake and written put the message themselves on the cake? It seems that the gays were just out looking to stir trouble.
How difficult would it be to find a homosexual cake decorator?