This is a entire new topic of debate, What I believe is that it owes much to Muslims not speaking much against such issues as well, 7/7 testomonies and many such stands as proof of some.
ground peoples be it Muslims or whoever are not educated enough to understand and differentiate between fundamentalism religion and terrorism.
to one general public Islamic terrorism can be "oh those bloody Muslims and their book" view, to some it can be "Aint we ally of one largest fundamentalist sponsorer?" , to another it can be "Look where are common Muslims against this, when common Christians are battling against Vatican orders?" , to me it is "Where is the reform? Muslim world need a reform that has happened in Europe more or less during WW2, If there was no fundamentalist supporter among common-Muslims you wouldnt have ataturk born or you wouldnt have terrorism being sponsored for 7/7, same for Christianity etc etc" To me the very concept of ummah is a highly communal thing which needs the first reform if any just like the xenophobia some Indians has of akhand bharat theory.
so dont generalize public opinion without knowing someone, most of the times they are just random thoughts and not analytical thoughts, if you ask a westerner to analyze vatican he will come down against it with lot of points albeit if hes rational thinker and a good religious fellow, how many Muslims will come and join against beheadal orders in Saudi? other than memri ofcourse.