"A Constitution is not intended to embody a particular economic theory, whether of paternalism and the organic relation of the citizen to the state or of laissez faire. It is made for people of fundamentally different views, and the accident of our finding certain opinions natural and familiar, or novel, and even shocking, ought not to conclude our judgement upon the question whether statutes embodying them conflict with the Constitution of the United States." [198 U.S. 75-6 (1905).
In short, the photographer had every right to not take on the job.
Christians are officially a lower caste than others