The “sincerely held religious belief” is a crutch that has been allowed only because white Christianity is the dominant religion in America. As I’m sure you are aware, some evangelicals sincerely believe that all birth control for women are abortifacients, even though most birth control works by blocking ovulation. They are demonstratively, scientifically wrong — but still are allowed to make policies that affect their employees based on this dogma.
Many evangelicals still sincerely believe that blacks are inferior and should not mix with or marry whites. And yet, we no longer allow that kind of belief to go unchecked. How is it that we have as a society come to realize that racism is not defensible, but still believe that other types of discrimination are OK due to a “sincerely held belief”?