“Would you be as quick to suggest that if you see (through the glass wall) your frum neighbor in McDonald’s fressing a cheeseburger, that we be assume he has a heter?”
That is an example of the type of inappropriate equivalency to which I was referring. Eating treif (and l’kaf zechus there might be a reason for it, i.e. a medical condition, if an otherwise frum person is doing it, as someone stated) is an absolute issur. A thing is kosher or it is not. A cheeseburger made with kosher cheese and kosher meat, is still assur for us. EVERYONE knows and agrees upon that, if they are shomrei Torah u’Mitzvos. Not so with skirt and sleeve lengths. It is not as black and white an issue, and to say otherwise, is to discredit all the VERY many poskim who held kulos. I have seen pictures of Rabbonim and their families, in the 1940s and 50s, where the daughters, who were adults in the pictures, wore cap sleeves or slightly longer. The Rabbonim, with long beards, and whose wives were wearing shaitlech (the OLD style, not like the natural-looking ones of today), permitted their daughters to dress in the customary style of all young women of that time. Again, I am not saying right or wrong, only stating an observation.
Whatever we each hold to be the proper way of doing things, we also have to recognize that just as we make a choice, someone else’s choice may be different from our own, and that does not make them not frum. If they desecrated the Shabbos, ate tarfus, and didn’t practice TH”M, then I would have something to discuss about their religious observance.