There is an entire "targetted individual" community on the internet.
You can tell that something has happened to them, but its ephemeral, because its psychological, and what do all of us do when we don't understand someone ?
We dismiss them. We other them. We isolate them. We walk away.
Not as a group decision, but the outcome of our collective individual decisions.
Abuse someone long enough, psychologically, and if they are not educated and self-aware, their behavior becomes erratic and they lose all social support.
It's not unlike veterans of a war, who understand what each other went through, when the public doesn't.
The "targeted individual" community is mostly people with paranoid delusions. That might not be the right medical term - I don't intend to diagnose people, just to describe what they are experiencing.
Unfortunately, our society is really good about detecting people who are "acting weird" - and some people decide to harass or bully the weird ones. Feeling like you are being stalked makes it very difficult to act "normally" in all circumstances, which increases the odds on any subsequent outing that somebody will notice and act toward you in a way that's undesirable.
It still sucks, what is happening to these people. But it's not a coordinated malicious campaign against them in particular. It's like you say - the outcome of our collective individual decisions. For most of them, there never was any "targeting."