When Does 'Extreme' Become 'Mainstream'?

Ed at Dispatches links to a post at Electric Venom about honor killings in the Islamic world. Usually I'm inclined to dismiss such incidents as non-representative ("the work of extremists" in journalistic parlance), but the linked-to post paints a very different picture. The incidents listed in the post are broadly distributed with respect to geography (and probably strain of practice as well, since one is correlated to some degree with the other^*). Additionally, the perpetrators do not seem to be particularly remarkable; the news accounts give no reason to believe that they are anything other than representative of their communities. These two observations strongly suggest that the beliefs/ideologies which lead to honor killings (and, presumably, other atrocities as well) are widespread at a grassroots level. Assuming that's true, is it appropriate to describe such activities as 'extreme' (or any of its permutations)? 'Extreme' is necessarily a relative label; if you're going to describe some behavior as 'extreme' its incumbent that the implied middle ground actually represent mainstream thought. It is still possible to argue that the above behavior is extreme in the sense that such behavior is relatively rare. But the ideological sense of the label 'extreme', that a view or behavior represents a fringe element, no longer seems to apply. So Ed, if you're reading this, would you still file the post under "Religious Extremism"?

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* My thesis falls apart, of course, if stonings and such can be traced to a particular strain of Islamic thought. The articles referenced in the source post weren't particularly instructive in this area; if anyone has better information I'm all ears.