Quite apart from what the science says, the sociology says that political movements need to believe in some kind of impending disaster, a Heideggerian
being-towards-death, to undergird their imperatives.
[WS:] I think this is pretty old stuff, early 1960s or so. It generalizes for a small subset of social movements - the so called millenary movements, which are predominantly religious in nature, but the lefties have their share of it too - to a much larger universe that does not hold millenary beliefs.
The newer approaches to movement participation - resource mobilization or social networks - make no such claims. The only "need" for movement participation is to have social connection to the movement itself, ideology is pretty irrelevant. Some argue that ideology is an outcome of movement participation -i.e. a person joins a movement because of his/her social connection to movement activists, and as he/she participates in movement activities, his/her beliefs and world-view are increasingly influenced by the movement ideology and practice (the so-called frame alignment hypothesis).
Wojtek