I agree this happens a lot, but it can and does usually involve a small group of delusional people. It is adult bullying and for all the same reasons kids do it. The people are typically insecure, they feel some sort of threat or the "getting together" to bully, harass, attack the one person is something that draws them together, makes them feel "apart of things," so to speak. Usually these types are not very bright, they have low social intelligence, they have too much time to kill because they aren't involved in things that matter.
Their bullying causes tremendous harm, they become insulated and reinforce the dangerous mentality. They become more and more aggressive, to the point of following the person.
They are the ones who hide behind dark tinted windows, but like one poster said, pulled into the light they show themselves to be the cowards they are and scurry away.
The big problem is the lack of training for law enforcement on the grassroots level about this type of thing, how to deal with it at the community level. The lack of knowing what to do makes the cops worse. Doing nothing emboldens all criminals, and their behavior does rise to a criminal act. The lack of local law enforcement which is the only option for most is more harmful. So cops need to be enlightened and trained about this and to this, how to deal with this, and to be told to aggressively enforce laws such as charging people with aggravated stalking. It is a crime. Instead the local dinks who wear a badge want to blow it off become they themselves are not savvy enough.
When any bully starts to buy and use all these devices you can get online to stalk innocent people, things go from bad to worse. The legislatures need to start addressing this type of thing, including a rule that prevents the police from abusing such things.
If there are no laws, then they need to be created that will enable lawyers to sue these bullies, because when they get hit in the pocketbook, that will put an end to their devastating tactics.