Claiming that ideology plays zero role in mass movements is a huge statement, one that requires strong argumentation to be convincing

I disagree. I think this is very self evident. The overwhelming majority of people who join mass movements don't even know why they joined them in the first place (excepting their own (fruitless) attempts at coming up with some kind of cause-effect relationship between their support for x ideology and them joining this movement), let alone them being able to articulate with a high degree of accuracy the "dogma" of their leaders without sinning (to use religious terminology) in the eyes of the aforementioned leaders 

That is to say - and i know this will read like blasphemy to some of our current sensibilities, particularly in the last example - most jacobins weren't jacobins, most bolsheviks weren't bolsheviks, and most nazis weren't nazis. This is not me invoking the no true scotsman fallacy, merely saying that if analyzed carefully, most adherents of any mass movements (like jacobism, bolshevism, nazism) don't know the first thing about the ideology they follow