Why shouldn’t he be forced to photograph things he doesn’t want to photograph? If he just photographed things he wanted to, it would be a hobby. He’s not hanging around weddings taking photos for fun. He’s being paid to do a job, and the job is the same whether it is two men, two women, or one of each.
Apply the same logic to someone who didn’t want to photograph Asian people. “Hey, I know you’re in love, but I don’t condone your marriage because my God says Asian people shouldn’t get married. Sorry.”
It’s not that he should be forced to work for people he hates. It’s that he should not be allowed to be in the business at all if he wants to discriminate against his clients.