It seems to go like this: an idealistic and intelligent person, who reads a lot and thinks a lot, falls in with leftist beliefs, usually as a university student. But this person never abandons his/her ability to think critically. At some later point the evidence starts challenging his/her worldview.
Because that worldview is so deeply held, the first challenges are successfully resisted. Then, growing experiences add to the doubt, and the pressure builds to the point where it just can't be denied. The person then makes tentative statements to that effect: initially, perhaps, just among friends; ultimately, in public.
The angry and dismissive reaction on the part of former colleagues and friends is always--always--a surprise; one might even say, a shock. And this experience takes on a life of its own by underlining all the previous doubts. If those colleagues can't even listen to the questions and doubts of a former friend and fellow-traveler, how open-minded can they be? The essentially closed nature of such a belief system--the heretofore discussed "circle dance"--becomes clear to the changer-in-the-making. And, once that line has been crossed, there does not appear to be any turning back.
No, indeed. How can you keep them down on the commune after they've seen the truth?