I would like to propose the hippies and the hippie period of
1964-1984 as the greatest voluntary human experiment in history. I have described some of the lessons from
this great experiment in an earlier extensive blog.
I want to comment on the overall experiment. The closest thing to the hippie experiment was the Israeli kibbutz. This involved several hundred thousands of people for over four generations. Today, the movement has few of the earlier communal values and yet it survives on a more modest scale. The kibbutz was of unique value to Israel and may never play a similar role anywhere else. The hippie experiment was much shorter in duration but included several million people, ranging from the 200,000 hard core hippies to the 25 million pot smokers and rock music lovers.
The French Revolution was a major experiment and a great tragedy because
it was founded on class hatred and failed. The same was true for every one of the half dozen tragic and involuntary
communist revolutions. 
There was a hippie experiment from 1885 to 1905, I wrote
about it in a book called Baby Boom Two. It was smaller and more politically focused. Out of that earlier hippy movement came the Progressive political party that still echoes in our lives.
We are going to have to come to terms with the great hippie experiment. The whole world learned a great deal from it. What have you written about it?