Probably for much the same reasons that non-muslims aren't taking to the streets; ISIS are hardly likely to stop this campaign because of a protest march.
http://www.brusselnieuws.be/nl/nieuws/jongeren-gooiden-stene...
And then this happens. What are we supposed to think ?
Assuming all Muslims are ideologically the same, and that Muslims monolithically defend this sort of behavior is an asinine assumption.
Your original post comes across as prototypical "us vs. them", "we are the good guys" blather. Yes, murder and violence are indefensible, but otherization does nothing to work towards deeper understanding of the causes/issues at play.
Plenty of Hacker News users claim it all the time, unfortunately.