WhyDoIEvenBother, I did not make this up. Please check out Halichos Bas Yisroel where the topic of tznius is discussed according to the poskim. The MIshna Berura states that one must only cover from the knee and above. When did following the MB become unacceptable? The discussion is based on the words zroa and shok. I totally agree that one who follows the more stringent definition that the shok includes the calf could not permit a slit. But then one must require ankle length skirts. However, to say that we follow the MB’s opinion that the shok is the thigh, and then come along and say that true, the skirt must only reach to below the knee (with a margin), however, if it contains a slit below that point it is treif is totally irrational. It is a simple kal vachomer that if the entire skirt could be missing below the margin and be kosher, then if just a slit is missing, and the rest is there, it is certainly kosher. Again, if your posek holds skirts must be ankle length, then come out and say it. But this is not what I have seen in camp clothing lists, where this silly contradiction in logic exists that they must only cover the knee, but slits are forbidden. The only logic there is that they are concerned about some styles where the slit goes far above the knee, and hence forbid all slits.
EyesOpen, the reason why I am so against creating new chumras, is that the primary problem facing the klal is the terrible fighting and sinah amongst groups. Conceivably a girl wearing a kosher slit could now find herself the target of acid throwers, or bus-beaters if this misconception is allowed to circulate. One who follows the mishna berura should not have to fear these loonies who are all too common these days. (Even one who does not follow the halacha correctly should not have to fear these loonies either.)
Even aside from that, why must we make divisions in the klal, where if a girl wears something kosher that is not what is worn in XYZ community, she should be the object of derision, not our type, more modern, etc.
As far as Bas Melech, one who follows the halacha is a Bas Melech. We do not have the authority to make up arbitrary rules not based in halacha and declare that one who does not keep them is inferior. I have seen on camp lists that the very long floor dragging skirts are also treif. Somebody decided that is not the yeshivishe thing to do, and invented a new halacha or minhag by which to look down on the other. In fact it has as much significance in the eyes of the RBSH as the color of a man’s suit or shirt, which is zero.