It is difficult to come up with only one reasons why people choose violence.
One of the reasons might be that they feel there is no alternative; that the only way their views can be expressed is through violence. In a way, I am sorry this person died as I think trying to learn why he choose this activity would be useful.
Throughout our history, there have been hundreds millions of people who are angry about stuff who do not choose violence. Why? Why not? And then we can apply that to these people who do choose violence.
If we can understand why (truly understand and not just make emotional generalizations) we might be in a better position to lessen instances of this sort of violence. We may never be able to eliminate it totally, but that should not be our only goal.
As previously posted, I agree that the Internet is an enabler. Prior to the Internet, we had crazy guys, but they tended to be lonely and mostly ignored by sane people. Other than "I would like to subscribe to your newsletter" the ability of these crazy guys to interact with other crazy guys was more limited.
Then came the Internet. The advantage of the internet is that everyone can share their opinions. The disadvantage of the internet is that everyone can share their opinions.
Now it is a lot easier for Crazy Guys to not only share their opinions but to virtually meet with other Crazy Guys. When Crazy Guys get together, even virtually, they can enforce and perpetuate the crazy. Crazy Guys get affirmation and a sense of community with other Crazy Guys. This can, in my opinion, embolden them.
These "lone wolf attacks" are really not made by "lone wolfs", but by members of an unorganized but emotionally supportive virtual group. I bet you a scooby snack that this guy was active on some nut-case forums where he was getting affirmation and confirmation bias that enabled him to justify such a terrible act.
So what can we do about this? Unfortunately not much.
Shaming and ridiculing the nutters won't do anything as they can find their affirmation from other nutters. For the same reason ignoring them won't work. It certainly does not work on this site nor would it work on other sites. Has anyone's radical/extreme opinion ever been changed because of a thread on an internet forum? Doubtful.
Restricting or monitoring the Internet? Yikes! that might be a case where the cure may be worse then the disease.
Which gets back to my original statement -- they feel there is no alternative; that the only way their views can be expressed is through violence. I don't know what the solution is.
Mature people recognize that sometimes elections don't go the way they want. In pretty much every presidential election, about half of the citizens are not happy.... but almost of them don't resort to violence. Why? But some do resort to violence. Why? Those are the questions we need to answer in order to start finding a solution, or more accurately solutions as I don't think this is a simple problem where one solution will take care of the problem. People are more complex and their motivations even more complexer
I feel it starts with everyone in our society taking a stand that this sort of political violence is not acceptable. Even the nutters have to understand that no matter what they vent on the Internets Tubes, political violence is never acceptable. We need to remove that level of affirmation. Easy to type, very hard to implement.
We may have to consider the possibility that this is an insolvable problem. We can't take the internet away, we can't suppress expression, we can't take away the guns...and we may not be able to affect the violent motivations.
JFK once said "Our problems are man-made, therefore they may be solved by man." May be solved, not always solvable.