I want to clarify a few things:
Of course it is a terrible thing to harass anyone unprovoked. And if someone sees such a thing, they should certainly be upset about it, and want to protest, and be upset if they see that there were witnesses who did not protest. If I saw people dressed in Frum attire harassing someone without prior provocation and I saw that there were others there who could have protested and didn’t, I would certainly be very upset!
However, there are several (perhaps understandable) misconceptions here:
1. The assumption that such things happen frequently. As it has already pointed out, that is far from the case.
2. The assumption that if someone is dressed a certain way, it shows something about their level of observance and the community to which they belong.
Years ago, there was another (similar-type) of issue that people were upset about. At the time, I was studying in a certain program in EY, and one of the students (who was a modern baalas teshuva) asked one of the Rabbanim (Dati Leumi and very, very anti-Chareidi) about it. He explained that these people aren’t even Frum, let alone Chareidi. They are people who went off the Derech and are no longer Frum, but still wear the levush.
I used to work in a school located in Geulah. Once on a Friday night, I saw a bunch of men yelling at a car driving by. I wanted to say something, but couldn’t say anything to them (I think I actually tried, but they didn’t hear me- they were too busy running after and shouting at the car), so instead I said something to a group of girls standing nearby. From the way they responded, it was clear that they were against such behavior as were the rest of the community, and that they did not consider these people to be part of the community.
So when you see someone engaging in anti-Torah behavior, don’t assume they are Chareidi just because of their clothes. Just like if you saw someone driving on Shabbos wearing Chareidi clothing (and it was clear that there was no pikuach nefesh involved), you wouldn’t call him Chareidi, don’t call this guy Chareidi.
Just like someone who drives on Shabbos is by definition not Chareidi, someone who harasses another unprovoked is not Chareidi!