Now imagine those "moms" being catched by their dads while dressed like that.
Society should indeed help each other to better behave within society itself, even enforce it sometimes, but not by apprehending how people express themselves. Free speech might be about govern reprehension but the govern is (or should be) just society ruling. Dressing, moving and talking are simple ways of self expression. You could argue punching in the face should also be covered by free speech rights, so where to draw the line? Well, while we don't change the whole system the line will keep moving. Laws are doomed to be abused, because they will always give a window for a new way of expression. And why people keep abusing it? For attention. Anything new brings attention.
And how can we change a system? "Just" effectively change any of the core variables in the vicious cycle.
people still have way too much sexual repressions. Centuries ago people would react just like that to a kid looking at a girl and smiling. Meanwhile, if it was a gag and there was a camera, they would both laugh. The only reason people get angry is the perceived reason behind it, and that's in the eye of the beholder who thinks the got all the answers to how everyone should behave.