Maybe they do so. There are well regulated channels for such protests. In my limited experience those who protest against human rights abuses are better-educated. By "better-educated" I mean educated so as not to be stultifyingly compliant for the sake of solidarity with the traditional group. In other words, most of the Muslims whom I see around are dressed as traditional Asian villagers would dress and look as if they are very docile people.As to the effectiveness of protesting about cleric and govt behaviour in Pakistan et al - any action, however small, is better then none, and it would also have an educational effect on Muslim youth in the UK if their elders demonstrated displeasure with supremacist intolerance.
My guess, and it's only a guess, is that better educated Muslims challenge human rights abuses equally as much as Christians, Humanists, and others.
Those 'Asians' who have ganged up on vulnerable white children are not so much Muslims as they are under-educated criminals who are as much alienated from family control as from control by mosque authority.It's not Islam that causes that criminality and alienation but other social factors. Islam is authoritarian and demands certain behaviours of which criminality is not one. Rather ask why Asian criminals ceased to observe Islam.