Even though many of the moderate Muslims might like to speak out in condemnation of ISIL, they don’t dare do so for fear of losing their heads.
....Or they sit on their hands in “silent support”.
If the so-called moderate Muslims are correct that only a tiny minority are radical Islamists, then they have nothing to fear. They outnumber the radicals 10 to 1. If they REALLY opposed the radicals, they could come out en masse with such a show of strength that the radicals would be powerless to stop them.
But that never happened, and it never will. First, the number of Muslims who support Sharia is WAY larger than 10%, more like 30%. These so-called “moderate” Muslims are not moderate. Radicals are running wild all over the world and the “moderates” are totally silent. Where are the moderate imams issuing fatwas against the radicals, saying in no uncertain terms that violence in the name of Allah will send you to hell? It’ll never happen, because they believe the exact opposite.
It’s a combination of assent, for the ones who say they oppose the Islamists but really don’t, and cowardice, for the ones who like you say, fear losing their heads.