Twofingers, I can totally see the point of that. It makes the person marching feel empowered and amongst friends and supported. That is why marches are good for civil rights issues/workers rights issues - because they show people they are not alone and encourage supportive behaviour.
They are completely ineffective at single issue policy decisions (Iraq war, hunting, tuition fees etc) because they don’t actually change minds from policy A to policy B.
It’s great that people feel they are doing something - but they probably aren’t.