Let's just flip that, shall we?
"Moderate muslims have allowed violent activists to hijack their cause and plan and carry out terrorist attacks frequently and violently for the past 10 years. As a result, they have lost all the goodwill ordinary white British people afforded them. Why did they allow them to do that all these years, and yesterday?"
It is not appropriate to blame moderate members of a group for the actions of extremists members of the group, nor to hold them responsible for those extremists.