Sure - he will sell you a cake as long as the cake is being used for something he agrees with.  Allowing this opens the door to any person refusing to sell a person anything if that person is going to be using it for any reason they dont agree with.  What if this Baker refused to sell a cake to an interracial couple getting married because he did not agree with that?  Is that better, or worse - or would you still be on this bakers side?  He is hiding behind his religion and saying he is not homophobic because he will sell them other stuff - he just wont sell them a cake they will use in their wedding.  So, its really no different than telling ANY person that you will not make this cake for them, because you dont agree with what they are doing.

The "specific message" he is against that he will make wedding cakes for everyone.  He wont, obviously.  He only wants to make them for straight couples.  That seems to be his only requirement.  Which, is textbook discrimination.