Perhaps part of the problem...
is that, from what I've heard, there isn't much of a formal Islamic leadership, at least not in the same way as the Catholics have a strong leader in the Pope. Islam seems to lack any form of central leadership to denounce what is being done in the name of the religion. There has been some denounciation from brave but isolated voices, but not enough, IMO. Perhaps it's a question of fearing reprisals but I honestly don't know. I can imagine that if I were a devout Muslim and someone was doing these terrible things in the name of my religion that I'd complain, but that's only a hypothetical situation.