Brookings Institute has a series of papers about Islamist movements around the world: https://www.brookings.edu/articles/rethinking-political-isla...
which includes both analyses from Western academics as well as responses from members of Islamist parties.
> It absolutely follows that intolerant populations can systematically elect intolerant leaders who then cause instability.
Intolerant of what, and what do you mean by "instability"? If the ideology of the political parties and institutions reflects that of the (vast) majority of the population, why would we expect "instability"?
Democracy can descend into demagoguery; I believe that occurs when the "people" feel like the state has been captured by an elite (oligarchy) that doesn't represent their interests (i.e. interests of the majority), "intolerant" or not - e.g. Gracchi brothers, Hugo Chavez, etc etc.