This is somewhat more “radical” than the Shakers who believed sex could be eliminated. These people just don’t have the patience of the Shakers. 
It’d be a shame if anyone attempted to talk them out of such a belief. Natural selection in its most direct form.
I can’t imagine that a Breatharian woman would be able to carry a child to term anyway. 
This reminds me of the recent thread about pregnant women dying because someone blew air into their vaginas.
Following some of the links you are drawn to the conclusion that they want to sell you a lot of special foods, vitamins, etc. so you can eventually reach the state of being able to live on air alone.
Except for the Adkins Breatharians - they don’t breathe Nitrogen, but they are allowed to have all the Carbon Dioxide they want.