GAW: But they are claiming that this is Halachah, not social construct.
No, Joseph claimed it was Halacha. He is wrong.
The “Neshei Belz” said that it is to avoid possible situations of Kaas and Nivul Peh. There is certainly no halachic basis for making up out of thin air such a middos-type action, but if they find that to be socially appealing to their sub-sect, who am I to complain?