DaMoshe
You do realize that the Chassidim are more machmir on Hilchos Tznius than the non Chassidish (or rather that they “keep” Hilchos Tzniyus vee es darft tzu zein)?
I am not Chassidish but I definitely applaud their lifestyle (most things at least) and think that with regards to certain things they got it right. The lack of Tzniyus and mingling by simchos and what not that goes on by the non Chassidish velt is utterly disgusting. I was recently by a “Yeshivish” vort and they had one of those half mechitza thingies where theres some trees here and there and the middle is divided by a table where if you just look up you can see the whole ladies section. If that wasnt enough there were women coming over into the mens section. Is this what Hashem wants from us? It has become so common place that by “shmorg” style events men and women mingle that we have forgotten that theres even something wrong with it.
I think anyone anti Tznius is actually someone who is not healthy in these areas and wants things to be in a non Torahdig not Kedushahdig way. I think on some level they feel threatened by others who control themselves in this area.