I asked a friend who happens to be an academic for some articles on why people LEAVE social movements. The literature is thin, as you’d expect.
One thing he sent me was “Some Elements of an Interactionist Approach to Political Disengagement” by a French academic called Olivier Fillieule.
Here’s a bit I read out to Mrs Towers
it is not always the longest standing members who find themselves marginalized when the composition of the collective organization changes. Many monographs show how, faced with the inflow of new members, longtime activists may, through various voluntary and involuntary means, ‘close ranks’ and make it difficult for newcomers to integrate. In research on internal decision-making procedures in American social movements, Polletta (2002) provides a number of examples of this. She especially shows how women’s liberation movement, based on an internal structure stressing sisterhood and rejecting explicit internal hierarchy, placed numerous barriers to the entrance of women anxious to join the group, to such an extent that generational renewal was rendered almost impossible. (Polletta, 2002: 151 and 154. See also Whittier (1995) on the feminist movement in Columbus (Ohio)
She said something like “Pope still catholic, activists still human” and that put me in mind of a something that I’d stumbled on earlier in the day when reading about Los Angeles’ police force (don’t ask). William H. Parker, police chief from 1950 to 1966 (and who coined the term Thin Blue Line) said in response to a corruption case
“We’ll always have cases like this because we have one big problem in selecting police officers … we have to recruit from the human race.”
And so it is with ‘non-hierarchical’ groupings. I only hold them to a higher standard because they are always bleating on about how they understand power. Hmm, they don’t understand invisible power so well…
dwighttowers.wordpress.com 
Well, I think that if you build a good small group, and establish a culture, a way og getting along and getting things done, then it can be very disruptive and discouraging to cope with a significant influx.
Rather than letting cells swell up till the membrane bursts, why not hive off?
Right on, Dwight, that nails the main reason people leave, let’s call them orginizations in general since you sourced cop depts. as well; the fact that members have to be human. Which begs the question of what might it be like if humans who actually have worked at the issues involved with the various power trips…might they/we manage to do things differently, and avoid the other big reason people leave, of course–“burnout”!?
Why not simply “hive off”, Vera? That’s a good standard to set–if the non-movement cannot easily do this, there’s probably a real problem. The temptation though, can be partly valid, because new groups, being not under the control of the better-established groups, can make for scary colleagues when they act all, well, “out of control”! …And then, whoops, there goes the movement/org… So that would seem to be one huge glaring advantage of a “culture shift” approach, eh?
Mm… ALF (and the Tea Partiers) have an answer to that, Jay D. They got several key agreements, and if a group acts against them, they have simply acted themselves out of the “un-movement.” As, for example, if a group claiming to be an Animal Liberation Front group commits violence against living beings rather than limiting it to property. Or a group masquerading as Tea Partiers extols leaders.