If this huge crowd of Christians had marched on mass that would make them politically active to a particular political cause... precisely what you, yourself, probably don't want the Church to do. 

The Church is not called to be politically active but to rather be part of building society. Of course people can (and in cases should) march when appropriate, but please never under the name of the Church, a Christian organisation, or under the leadership of a purely Christian leader. What you get there is everything you probably don't want.