In reading around the net on differences between Sunni and Shia Muslims when it comesto extremism, I found this article written a couple of years ago. It makes sense to me. Here:
http://www.theamericanconservative.com/sunni-and-shia-terror-a-difference-that-matters/Shia and Sunni extremism do not express themselves the same way, it seems. The Wahabbi Salafist nonsense (Sunni extremism) is the stuff everyone across the globe is dealing with in some form, from Al-Shabaab to Boko Haram to Al-Qaeda to the Pakistani Taliban groups and Chechen ones in Russia to the ones in India and the Philipines and Indonesia, to the monster ISIS/ISIL to the random attacks in the West, like the idiot who beheaded a soldier on the streets of London.
But we hardly ever encounter Shia extremism in any form outside Iran/Iraq where the majority population is Shia and itaexpression even then tends to sectarian violence with Sunnis. This writer says that Shia extremism is more organizational/state-centered with tangible regime-based goals. Very political, sophisticated too. He says it is much more akin to the IRA than your typical Wahabbi suicide-bomber/decapitator. I think it makes sense.
Compare fighter groups like Hezbollah (Shia) and Hamas (Sunni) for example, that many would consider to have legitimate causes. Both have essentially been engaged in the same struggle against Israel on behalf of Palestinians. At least, this was the case before the current CIA-inspired Mid-Eastern chaos drew them to Syria to fight Sunni fighters in aid of Asad, Iran's ally.
But in terms of organization and operations and methods of warfare, Hezbollah is much more like a typical army than Hamas. And despite Iran having become one of America's enemies since the Shah was deposed in 79, you never hear of a Shiah Muslim randomly killing a person simply because he's in some kind of abominable/unacceptable religious tradition or lack thereof, including foreigners in their midst. The suffering of Iranians, like Saudis, has much to do with the state itself, like in any typical dictatorship,except this particular kind has a religious expression like in mideveal Europe.
That author thought back then (2013) that lumping Shiahs and Sunnis together (when speaking of extremism) was a mistake. He seems to think that Shiahs, even extremist ones, are in general much less whacko than Wahabbi terrorists. He would appear to think it much easier/wiser to negotiate and ally with Iranians (much to Isreal's chagrin) than any brand of Salafist Jihadism. Having seen the kind of world ISIS is ushering into the world, I tend to agree.
Majority Sunnis in Egypt are totally anti-ISIS. (They get like 3-4% approval rating in Egypt, a majority Sunni country). I think majority Sunnis elsewhere are the same way. In fact, my understanding is that without the rich Saudis indirectly supporting/sponsoring Wahabbism (a kind of radical revolution that took place within Sunni Islam in Saudi Arabia about a century ago kinda like an Islamic "protestantism" as I've seen it described, and not at all the majority in Sunni Islam) much of modern Sunni terrorism wouldn't exist.
Obama recently got into trouble for declining to admit that ISIS were Islamic. I think it's better to call them Wahabbi extremists (though Al-Qaeda would protest!) or if not then at most, Sunni extremists, rather than simply pretending that it is not religion that motivates ISIS. It is religion, but it is just one ( a minority, even within Sunni Islam) among the expressions of Islam.
http://www.theamericanconservative.com/sunni-and-shia-terror-a-difference-that-matters/