Research suggest that what makes an activist is not conviction or personality, but social connections. People get drawn to action by their friends, spouses, syblings, or co-workers, but then they rationalize their participation in terms of their adherence to the action's ideology. Ideology or personality alone seldom acts as sufficient motivator (ditto for most kinds of volunteering).
And that makes perfect sense. The behavioral model that seems to have most validity is not utility maximization, but transaction cost minimization. People tend to do not what gets them the most benefits, but what comes easiest and offers the least resistance. Thus, to induce people to action, one need to lower their transaction costs (that is, btw, why most business firms offer an 800 number). Social conncetion do reduce transaction cost of social activism, hence they are a good "motivator" for participation.
Wojtek