"As far as it being due to his religious beliefs, the other problem he runs into would be that it is unlikely he checks to make sure none of his heterosexual couples have committed sinful acts." That's a judgment of how he chooses to practice his religion. You may find it inconsistent but it isn't up to you. 

Some say it's inconsistent to make a wedding cake for a couple living together. But in fact the wedding celebrates the end of that particular sin. Nonetheless, he can believe as he chooses. He doesn't do Halloween cakes. Something other Christians might view differently. That isn't for government or anyone else to decide is right or wrong religious belief for another person.