Islamist groups have certainly gotten the "best" press for a while and have the most prominent groups whose stated goals essentially boil down to "world domination" (but their plans for world domination have only slightly less chance of success than mine, so relax on that front). That, however tells us exactly nothing about the propensity of Muslims to become extremists.
Extremism is no more common among muslims than it is among any other large group unless you limit your definition of extremists to Islamic extremists.
Edit: grammar.
But this is way off topic and my argument has nothing to do with Islam. I'm just pointing out how easy it is for us to play couch sociologists when weighing the merits and problems of "Engineering" culture, vs how difficult it is to hold a similar discussion about the issues of "standard" religions or cultures.
P(Muslim | Terrorist the US currently gives a shit about) is interesting, especially given the propensity to regard certain terrorist groups as criminal elements for political reasons.
Also interesting, other countries sometimes negotiate disliked groups onto our lists to legitimize their crackdowns (ironically the crackdowns can push the group to actually become terrorists. Hi Turkey!) and make their international fundraising efforts effectively illegal.
It is important to refute you because the implicit points when you talk about "how difficult it is to hold a similar discussion about the issues of "standard" religions or cultures". It isn't difficult for scholarship to have that discussion. It has been had. It disagrees with what you suggest to be true.