Here's the thing: the vast majority of trolls and people who make threats are not "psychos". That is the truly terrifying thing. Most racists are not mentally ill or brain-damaged. Most violence in the world isn't carried out by clinical psychopaths. Completely ordinary and healthy human beings are capable of performing acts of terrible cruelty and violence. Why? Because of their environment. Their culture.
Passing off all of this as the actions of "psychos" is just burying your head int he sand. Internet trolling and threats is the product of an internet culture that has evolved, and by extension, that means that a lot of people who don't actively participate in that activity do share in the responsibility for maintaining that underlying culture.
To make an analogy: racism is still endemic in the United States. That racism is far too broadly practiced to pass off as the actions of a few random nut-jobs. Instead, it is cultural: the product of information and teaching that is passed from person to person, generation to generation. People partake in racism because they are taught that it is natural way of things, and even those who don't actively participate don't question it because it is "the way things are". As long as people can rationalize that events are logical or normal, they will happily pretend that they are not happening at all, simply because it doesn't directly affect them.
We are at a similar point with internet trolling: it is so common-place that people simply accept that it is the natural way of things, without actually examining the state of affairs. Trolling and internet threats didn't always exist; they are a phenomenon that evolved. Back when the word "trolling" was coined, it took a very different form: people trying to 'catch' newcomers to message boards who were not familiar with the local memes. Those were mostly harmless forum in-jokes, but the phenomenon evolved from there to become groups intentionally trying to rile up and inflict emotional harm on other groups.
I can't say I know the whole story, or really where the root of the problem is, but I don't want to just pass this whole detestable situation off as something that can't be changed. I don't want to go and pretend that this problem has nothing to do with me. If left alone, it will fester and grow worse. It really will become "the way things are" and become all the harder to root out.
If you have been the victim of threats and harassment online, you should sympathize with the goal of changing this problem.