I am sufficiently egocentric to conclude that Froggie is responding to my post immediately above his.
As to his/her comment (B): The problem you highlight is no different that conflicting opinions of rabbis, and the solution is the same: choose one and stick with it.
As to his/her comment (C): I was addressing the institutions that call themselves yeshivas. As you and I agree, personal health is both a secular and a religious subject. I presumed – perhaps incorrectly – that yeshivas teach, at least in their secular curricula, some fundamentals of personal hygiene, in the lower grades. There are 2 values to such a subject: (i) improving the hygiene of kids with indifferent parents (which may not be significant factor among yeshiva parents), and (ii) giving an introduction to the science of health and medicine, which boosts secular education and may even provide a spark, in the future, for parnassah.