"The doctors actually could have a solid, non-religious reason for their reluctance to artificially inseminate an unmarried woman: the doctors might believe that children need a father, and are entitled to have a relationship with their father. We should not criminalize that belief."
As a matter of fact, that is exactly what these doctors' policy was, i.e., not to practice certain forms of artificial reproduction on single women. But the plaintiff in this case alleged it was because she was a lesbian, not because she was single. At the time, discrimination on the basis of marital status was not covered by the statute. Now it is. So now a doctor who does ART has to serve single women on the same basis as married women.
So marital status is now a protected class.