> Admittedly having not read the 400-page study […]

It is not a 400-page study: it is a 400-page book that goes over the research available at the time and summarizes it. The book leans slightly academic, but it's a fairly easy read.

A movement's success is (partly?) determined by its size and how much of the general population gets on board with the original (presumably) small group that started it.

* https://en.wikipedia.org/wiki/3.5%25_rule

The/A thesis of the author is that people are turned off by the use of violence/force and are less likely to agree with, and/or get involved in, movements that use violence.

So if a movement wants to grow the 'coalition' of people that will help and/or join them, that growth is best achieved by eschewing violence as much as possible.

[Edited GP post to add some of this comment.]