It's the functionality of clothes. We, society, assigns a value, a meaning to things. All sorts of things, every thing, everywhere, everywhen. Each society, by era, geography, etc, has its own mores and everyone within that society learns them and live within them publicly.
People who do not are by social definition 'abherrant'. Sometimes that is unfair, mental health, disability etc. Sometimes it is a matter of choice and aberration is just a bit amusing. Other times it's tediously annoying, infuriating.
And this is one of those tedious times. Underwear is just that. A glimpse of bra strap is one thing, flash of knickers is another. But swishing up and down a main thoroughfare in your best Victoria's Secrets is exhibitionism, even if you do think you are Clark Kent's female alter ego! And exhibitionism is a social no no, for many reasons. Some good, some prudish, but all known.
So all these ladies need to understand is what they expected to get out of this, what did they want from it?
Because the things they are smirking about, giggling over, getting all self-righteous about are the very basic social mores that protect women, kids, vulnerable people from being abused. We can wear the equivalent clothing, skimpy shorts and a strappy top, outer clothing, even if lacy, us outer clothing. But underwear, black, lacy, the sort associated with sex not comfort, is always going to elicit that response when seen out in public.
So apart from "No shit, Sherlock" what do they want from this? Sex work is work? Women should be able to wear arseless knickers and see through bras and be neither cold nor stared at? Not judged as a tad odd? What?