This baker wasn't "discriminating" based on these people being gay,  apparently he had baked cakes or done business with them before. His religion says homosexual marriage isn't acceptable, despite the fact that this country gave them the legal right to marry a few years ago. IOW, it's not like discriminating against a black person a woman, or even a gay person, it's deciding not to partake in an act that the baker  finds unacceptable according to the tenets of his religion. This couple could have gone down the street to buy a cake for their wedding, there was nothing saying they had to give this baker their business and force him to do something which was against his religious beliefs.