On that page there is lots of evidence from islamic sources clarifying that's isis are not islamic, using islamic text and literary evidence. In fact there are hundreds of groups across the world on fb which are similar.
and there is plenty in the koran to support IS. that's part of the problem. it's just plain wishful thinking to think the koran is all love and fun. so who's right?
I have Muslim friends and colleagues who are horrified. I do feel Muslims are being singled out by people (including those on this thread). Why were e there not hebdo-esque marches after the Charleston shootings? Why were white supremacists not asked to march. I'm white myself and it's clear that there is always always a more global outpouring of sympathy for white western victims of any crime. And if the perpetrators are white there is always less collective culpability.
I don't doubt many muslims are horrified. I also agree that there is more outrage when victims are white, but that's a separate problem. I don't really understand your point about white supremacists. Nobody is asking them to march because they are probably on the side of the shooter. They agree with what's happened.
The reason that muslims in general are asked to speak up about IS and extremists is that moderates and extremists share one crucial thing; islam (and it's associated texts). it's that shared ideology that one group is using to justify terrible violence. Both groups to some extent believe that islam and the koran are in some way very special books, and this belief and advocating it is entirely voluntary. Thus, it seems to me, moderate muslims (many of whom claim the koran is the greatest book, muhammed is the perfect example of how to lead ones life etc etc) need to somehow explain or find a narrative on why the violent bits of the koran and hadith (which are certainly there. you just need to read it) should be ignored.
The other problem is that even mainstream muslims support some deeply troubling ideas. Various polls suggest this.