***Why has this not happened?***
I am assuming you mean, "Why have we not solved the problem of violence which results from misunderstanding which results from mis-communication which should be solvable by patient civil discourse?"
***Any guesses (elaborate if you can)?***
Here's my guess: People don't read enough history.
Elaboration: People naturally view history parochially, as they do most everything else. This distorts their view, makes them and their people seem to be the good guys and the other people the bad guys. This breeds hostility and violence.
If everyone would read a lot of history, particularly histories written from others' points of view, I believe a fairly consistent pattern of human progress (yes, progress) would slowly emerge in the minds of the people.
That pattern of progress would show that for about a couple hundred thousand years, humans have taken a distinctly different approach to the problem of providing food and protection for themselves than that of any other species. That is by applying intellect, first to a discovery of how nature behaves, and second to exploitation of that knowledge to secure food and protection. As with the strategies of all other species, competition was at work selecting out the best tactics. So, we have had a couple hundred thousand years of competition (wars, crime, politics, etc.) of various ways of providing what we need, bringing us to the present day.
If you look at that big picture and ask, what have we been struggling to achieve all these years, I think you will have to acknowledge that we have accomplished it. We have solved all problems threatening our survival with the exception of threats coming from ourselves and the threat of an asteroid hit. It looks like we will have the ability to predict an asteroid collision in time to be able to divert it, so that only leaves man's inhumanity to man as the single problem left to solve.
Of course, without an understanding of history and our place in it, people still think that we have to compete with each other in order to get food. And, of course we still do. But not because we can't and don't produce enough, but because those vestigial competitive mechanisms are still very active in virtually all social institutions.
I think that if a person studies enough history, they will come to the inevitable conclusion that what we are doing is stupid, and that we should immediately start helping each other instead of trying to get more for ourselves.
I know that sounds simplistic and pollyannaie, and I don't claim to know how to get everyone to read enough history. But I think there is hope anyway.
***I think that we (as humans) will reach a consensus, but I do not know when, how, or by what means.***
I don't know either, but here's how I think it will happen. If you look at what happened to the world starting at about 1500 AD, you could say it was because of Columbus, or because the Muslims were finally driven out of Spain, or that civilized people finally got firearms that were effective against barbarians or whatever. But I think the single thing more important than any of those was the invention of Gutenberg's press. When people began to get information in print, they set to work challenging things like the divine right of kings, the authority of Aristotle and the Vatican, the reality of goblins, and who knows what else. They started on the explosive path which led to our modern industrial and information society.
Now, if you compare Gutenberg's press with our modern computer and communications systems including radio, TV, telephones, faxes, the Internet, and all the rest, it is easy to see that the entire population of the world has, or soon will have, access to up to date information many orders of magnitude beyond that provided by Gutenberg's books. Should we not expect a concomitant explosion in our progress toward solving our problems? It took us a couple hundred thousand years to solve the problem of getting enough food, and we did that in just the past 500 years. My guess is that it shouldn't take us more than 50 years to solve the problem of man's inhumanity to man. Not only that, I expect that most of us will be around to see it.
You asked, Phillip, and I answered.