Handfulls of demonstrators may not directly alter government policies, but they do serve as an irritant. If nothing else it spoils the day of a minister to the extent that he calls the police to break the demonstration up, so even a small protest reminds him that opposition does exist. People who regard such protests as meaningless should imagine how much happier that minister would be if they never had to face the protesters. When they travel to an armourments factory or announce a cut in funding they must think, Oh I do hope I don't have a mob of protestors today. These people are human, and they'd rather be greeted by dignitaries shaking their hands, without a howling posse of dissidents waving placards and drowning out their sycophantic speaches with a megaphone.