Such individuals, unless suffering from extreme psychological dissonance, must have something, some background set of habits or conditioned responses which facilitate their “triggering” in the absence of group induced motivation. The individual’s actions, however, must still be seen a part of a wider and more normatively permissive background. When you say MOST Muslims are unlikely to suffer from SJS in the future I wonder how you know who they are and how you can be so certain they won’t; no doubt similar questions are being asked about the former pro-American, naturalised, and culturally assimilated Hasan by his superiors in the US Army.
These background habits and responses are part of all of us. What triggers anyone to mass murder is of necessity both deeply individual and part of their social milieu. That Islam was part of Hasan's is undoubted. That Christianity and right-wing politics was part of that of someone like Tim McVeigh, OTOH, is also undoubted. You ask how can one be sure that MOST Muslims won't go out and shoot everyone in the immediate vicinity in the near future. How can you be sure that any white male who holds right wing views won't do the same? Or any alienated white suburban youth, etc. etc.

Furthermore, I don’t quite see how a totalistic worldview that entitles itself Islam or, Subit! in literal English translation, can be anything other than conflict prone at its heart.
Have you ever been to a Christian church in your life? Are you at all familiar with the history of Christian European expansion in North and South America, Africa, or Asia?

Neither do I see the injunction regarding Jihad as medieval only. They are part and parcel of Islam. The Sharia, the Quran and the Hadeeth are, Islamically speaking, universal timeless Truths. The injunctions are thereby not applicable to one historical circumstance but for all time.
There are also several different legal schools of sharia, and a quite significant population of Muslims do not accept the hadith at all. To say that there is debate over the validity of certain hadith and the varied interpretations of such within mainstream Sunni theology is quite an underestimation.

A few years ago one of the Imams at Al-Azhar in Egypt issued a fatwa requiring women to breast feed their male colleagues! In doing so working women would become nursing mothers to their male colleagues and thereby (supposedly) eliminate the risk of zinna (unlawful sexual intercourse). How’s that for a modern resolution of Islam’s take of women in the workplace?
Are you aware how many scholars work at al-Azhar, and how many fatwas are issued every day? Fatwas being legal opinions, of course. As for the breast-feeding fatwa, this was mocked throughout the region, condemned in Egypt, and quickly retracted by the scholar in question.

A Saudi imam recently issued a fatwa banning cell phones. I'm sure thousands of fatwas have been issued in favor of cell phones. If you've ever been to the Middle East, which fatwa do you think will actually be obeyed?