Unfortunately you would have to eliminate a huge % of humanity to achieve the first choice, NI. And then declassify atheism and humanism as belief systems. Starts to get complicated. Iron as champs seems more realistic.
Atheism is NOT a belief system. The very structure of the word tells you that!
Why would you have to eliminate sections of humanity? Is that what happened in the past? The religions of the Babylonians, Egyptians, Greeks, Romans, Norse, Celts, Aztecs, Mayans and countless others are now nothing more than mythology. One day Christianity, Islam and Judaism will follow the same path.
I’d just prefer that it was sooner rather than later.