The idea that you shouldn't be able to fire someone for their beliefs is stupid.
I'd like to use a better word than "stupid" in this article, but that's exactly what is; unintelligent, dense, brainless, and foolish. I'd also like clarify and say, "if those beliefs prevent you from doing the job you are being paid to do".
The fact is that anyone can claim that anything is a "sincerely held belief". Do you believe in "Thetans"? Most Scientologists "sincerely" do. What about the old Norse gods, or the World Turtle? These are all real belief systems (or components thereof) and if they are followed closely, would require someone to alter the things they do at work.
Now, let's get really ridiculous for a moment. What if I was hired as a fireman and later revealed in my heart that I felt that fires are best left to burn themselves out? How about something simpler like I am a radio personality that thinks I should be able to play TOOL nonstop for days on end? Yes, that's a cool proposition, but it's not what the owners of my workplace pay me to do.
What this comes down to, is "good lawyering" and people making very sketchy moral judgments not because they are right, but because it's a win for their "team" (the people who their beliefs align with).
If you're a pharmacist and you don't want to give out certain drugs, then go open your own pharmacy. If you're a nurse and you don't want to help certain people, go start your own home health company. If you're a d.j. who's positive that people want to hear TOOL back to back for days on end, then go buy a radio station. What you "believe" does not matter. You are paid to do a job, so do that job, or find one that aligns with your beliefs.
People who make these claims are just virtue signaling to the world. You're stupid if you took a job that goes against your beliefs. Get lost and let your employer hire someone who's good at it.